The Age Of ReasonThe 18th century is sometimes known as the Age of Reason, with style becoming all-important in art and architecture.154 Patrons began to choose styles at a whim and to discard the traditional love of classical Greek designs and themes. This Age of Reason was also typified by the gentle decline in importance of the aristocracy and a gradual rise in stature of the ordinary members of society.155 William Hogarth (1697-1764) was a painter of this era who painted satirical views on society with a moral message.156,157 As the 18th century progressed, painters began to search for new subject matter, which differed from the time-honoured themes of biblical scenes and portraits. Many artistic assumptions were destroyed by the French Revolution of 1789, which brought about a whole new way of thinking in Europe.158
Artistic styles ceased to be accepted without question, and art itself was no longer regarded as a craft; instead it became an academic subject.159 Painters no longer learned their skills with a master but instead would attend an academy of art, where they would methodically learn all the techniques of art from history. These academies began staging exhibitions in the leading cities of Europe, and buyers from polite society would attend and view the works on offer. Artists had to learn new skills in order to attract these buyers in an exhibition and many adopted bold colours and melodramatic themes to acquire attention. These changes in the place of art in society had many repercussions on the whole world of the artist.160 Traditionally artists had always produced their own pigments and paints. Recipes for these colours were handed down from master to apprentice over the generations, and were often closely guarded secrets. With the advent of art academies and an increase in the number of amateur painters simply painting for enjoyment, there arose a place for someone to supply pigments and colours to the art community.161 The new trade of the artist's colourman began, with businesses being set up to supply pigments, paints, brushes, canvases and all other materials to the professional and amateur artist alike.41,82
The beginnings of industrialization in Europe also influenced the world of art, and many dazzling scientific discoveries made in the field of chemistry rapidly unfolded to yield new and exciting pigments for the artist's palette.162 Artists were sometimes slow to take up these new discoveries, but as more new pigments were discovered the artist's colourmen really came into a world of their own.16
The Industrial AgeThe industrial history of pigments can be said to have begun between 1704 and 1710 with the synthesis of the first synthetic inorganic pigment: Prussian blue.163 The pigment was discovered accidentally by a Berlin colour maker named Diesbach.164 While working on the synthesis of a red lake from cochineal, ferrous sulphate and alkali, he ran short of potash. He asked a nearby alchemist named Dippel if he could have some potash to continue with his reaction. The resulting lake obtained was very pale indeed, and when Diesbach tried to concentrate it the mixture turned purple, then deep blue. Diesbach later realized that the potash he had borrowed had been contaminated with animal oil from one of Dippel's experiments, and had actually been set aside to throw away.17 After working out what had occurred, the blue impurity was identified as Prussian blue.17 The method for making Prussian blue was kept a secret until 1724 when it was finally published by a chemist named Stahl.164 Prussian blue was the first synthetic blue pigment that could be used in place of ultramarine, although it was susceptible to attack by alkali. The main benefit of Prussian blue was the price, which was only a tenth that of ultramarine, and it was thus very attractive to artists of the time.
Advances in ChemistryThe discovery of new elements played an important role in the discovery of new pigments around this time163, one of the most important elements discovered being chromium.162
In 1770 a beautiful orange mineral named chrocoite was found in the mountains of Siberia, and it rapidly became popular with collectors in Europe. The French chemist Nicholas Louis Vauquelin (1763-1829)151 obtained a sample of the mineral and analysed it in 1797. He discovered that chrocoite contained an unknown element that formed a variety of intense red, yellow and green precipitates.164 The new element was named chrôme from the Greek word meaning coloured. Vauquelin initially had trouble procuring chromium ores, but by 1809 a source had been found in France, and the bright yellow pigment lead chromate was synthesized.164 Some time seems to have elapsed before the widespread production of chrome yellow for the artist's colour market. The first person to manufacture the pigment in England was a Dr Bollman (1769-1821)163, a German-trained medic, strongly influenced by the revolutionary ideas of Europe, who took part in several political acts and was exiled from Germany for a while, after which he eventually settled in England. Bollman became interested in manufacturing chemistry and set up a pigment factory on the Thames at Battersea producing, among other things, chrome yellow. The pigment was very popular indeed, and Princess Charlotte had her carriage painted with the flamboyant colour, which perhaps started the trend of the yellow taxi cab later in history.16
During the course of his experiments Vauquelin also discovered chromic oxide, and he published the first account of this green pigment in 1809.162 In this paper Vauquelin describes the manufacture of chromic oxide by calcining potassium dichromate in a furnace. Chromic oxide was being used in the ceramics industry at this time but was later introduced for artists' use; it was considered to be a very reliable green pigment with excellent fastness properties but poor colour strength. In 1838 the French colour maker Pannetier developed a stronger, more transparent variety of hydrated chromic oxide, known as viridian82, which became very popular with artists and is still widely used today.30 Vauquelin carried out many experiments with chromium and discovered several compounds that were also used as pigments.
French UltramarineAt the beginning of the 19th century, as at all times in history, the demand for natural ultramarine far outweighed supply. The best quality lapis lazuli was mined in the Kokcha valley of Afghanistan, which was a very inaccessible region, forcing the cost of the pigment even higher than usual. So there was ample reason to turn the resources of the burgeoning science of chemistry towards the synthesis of this pigment.
Analytical experiments carried out at the end of the 18th century showed that ultramarine was composed of soda, silica, alumina and sulphur. By 1806 two French chemists, Desormes and Clément, had found that a blue impurity occurred in the slag of soda furnaces and had shown it to be chemically similar to ultramarine.162 This discovery led to a number of scientific prizes being offered to anyone who could devise a method of making artificial ultramarine. The Société d'Encouragement pour l'Industrie Nationale offered a prize of six thousand francs in 1824 to anyone who could make the pigment for less than three hundred francs per kilo.165 Four years later the prize was claimed by the French manufacturer Guimet who did not reveal his method.164 The synthesis of ultramarine was later published by a German chemist named Gmelin, who had discovered the method independently. Full-scale industrial production of the blue pigment was begun immediately16, and French ultramarine was widely used by artists.82 Natural ultramarine, however, is still considered to be superior for the purposes of fine art, despite its high price.
Green PigmentsSeveral green, copper-based pigments were being produced in the late 18th and early 19th centuries that came about by the chemical investigation of new elements. The Swedish chemist Scheele manufactured a green pigment of copper arsenite in 1775.151 This pigment was named Scheele's green and was discovered during investigations into arsenic.162 Details of the discovery were not published until 1778 by the Stockholm Academy of Sciences.165 To manufacture the green pigment some potash and arsenic oxide were dissolved in water and heated; then the solution was added slowly to a warm solution of copper sulphate to precipitate copper arsenite. Scheele warned of the toxic nature of the green substance, but it was accepted as an artist's pigment, being patented in Britain in 1812.16
Efforts to improve upon Scheele's green produced another highly toxic green pigment known as emerald green.82 This was copper acetoarsenite and was first manufactured commercially by Russ and Sattler in 1814. Emerald green was made by dissolving the pigment verdigris in warm vinegar, then adding a solution of arsenic oxide slowly to form a green precipitate. The precipitate was then boiled in fresh vinegar to obtain the bright green colour characteristic of emerald green.163 The pigment was a very popular colour but had only limited use in art due to its tendency to turn black on exposure to heat, and because of its highly toxic nature. Emerald green was widely used in wallpaper printing. A number of fatalities caused the poisonous nature of the pigment to be fully realized, and it then began to double as a highly effective rat poison in the home. On a slightly more sinister note, emerald green was featured in several murder cases, and unbelievably was still in use until the 1960s!166
Late 18th CenturyThe French Revolution of 1789 and subsequent industrialization changed the place of art in French society, but also changed painting styles throughout Europe.158 One of the most famous painters of this time was Francisco Goya (1746-1828)167, who became court painter to the Spanish royal family in Madrid. Goya produced works inspired by his own vivid imagination, and this represented a whole new concept in subject matter for the artist of the day.168
Also working around this time were two English painters, Joseph Mallord William Turner (1775-1851)169,170 and John Constable (1776-1837)171,172, who were both landscape painters but adopted very different styles from each other. Turner produced fantastic, swirling land- and sea-scapes with strangely lit skies, while Constable set out to paint exactly what he could see with his own eyes. Constable was one of the first famous painters actually to go outside the studio and paint scenes using the colours he saw in the real world. He was not a popular painter at the time and was often criticized, which is surprising in light of his continued popularity today. Turner was, and still is, regarded as one of the greatest colourists. He is known to have used a wide variety of pigments. Analysis of his watercolour box has shown a large range of pigments, including several chrome yellows, cobalt blue, blue verditer, chalk, Indian yellow, red madder, yellow ochre, vermilion, red ochre, raw sienna, gamboge and carmine (presumably from cochineal, although the reference is not explicit).17 Turner used many of the experimental pigments of his time to great effect in his works.
New PigmentsZinc white, or zinc oxide18, was introduced as a pigment from the beginning of the 19th century although the substance had been known since antiquity.173 Zinc oxide was a by-product obtained from the production of brass, where copper and zinc spar were heated in a furnace174, and was used for medicinal purposes.175,176 Zinc white came to prominence as a pigment after the element zinc was isolated and identified by Henckel in 1721151, which allowed a production route for pure zinc oxide to be investigated. Metallic zinc was calcined in a furnace in the presence of air to form zinc oxide.177 Another reason for the introduction of zinc oxide as a pigment was because of concerns about the toxicity of lead.178 The primitive production methods used to make lead white were causing an increasing number of cases of poisoning179, and a replacement white pigment was needed. The first attempts to introduce zinc white as a pigment were in 1780 but it failed due to the substantially lower price of lead white. Zinc oxide did not become popular as a pigment until it was introduced by Winsor and Newton in 1834 under the name of Chinese white.180 Zinc white was not highly recommended by artists except for watercolours, as it is transparent in oils and is also a poor drier.59
Cobalt green was invented in 1780 by the Swedish chemist Rinman59,162, but was not widely used for about another 50 years. It was made by forming an aqueous solution of cobalt and zinc nitrates, then adding an alkaline carbonate and heating strongly to form a precipitate. The bright green precipitate had good pigment properties but fairly low colour strength.16 Cobalt green was only produced commercially after zinc oxide became widely available in sufficient quantities for the manufacture to become economic. It was introduced as an artist's pigment in 1835 and is still used today.
Coal Tar ColoursDuring the Victorian era a very serious revolution in colour history also took place. It began when August Wilhelm Hofmann (1818-92) identified the organic chemical aniline in coal tar in 1843.162,181 At this time Hofmann was working as a chemist in Germany, but two years after his discovery he became the first director of the Royal College of Chemistry in London. In 1853 Hofmann took on the 15-year-old William Perkin as a student of chemistry, and Perkin showed such a natural aptitude for chemistry that he was quickly promoted to the position of honorary research assistant.182 During the course of his studies, Perkin carried out a project attempting the synthesis of quinine from aniline. During the college's summer vacation, Perkin built a laboratory at home in which to perform his experiments. At this time the structure of organic molecules was a great mystery to chemists, and most research was carried out purely by trial and error. Perkin's experiments with quinine were not successful. However, instead of synthesizing quinine he did manage to produce a black precipitate that yielded a bright purple solution in methylated spirits.183 Perkin recognized the potential of this discovery as a dyestuff. He set about testing his product as a dye, fording that it dyed silk a beautiful deep purple shade that was very resistant to light.184
Perkin's purple product was the first synthetic organic colorant, named mauveine. It was tested industrially and patented.185 Perkin then rapidly resigned his academic position to set up as an entrepreneur of dyestuff manufacturing.1,186 The discovery occurred at a time when there was huge industrial expansion in Europe, particularly in the textile trade, and also a broadening of horizons as the rest of the world became more accessible to the average person.187 The Victorians acquired a taste for all things oriental, and purple became associated with oriental style.188 Consequently, mauveine became a great success as a dye and helped to set new fashion trends along with the crinoline, which had only been introduced three years earlier.189 Mauveine was not just popular as a dyestuff but was also laked to produce a widely used pigment.190 The bright purple pigment was popular with artists because of its unusual colour, and it was also widely used in decorative paints for the home by well-to-do Victorians. The discovery and synthesis of mauveine changed the world of colorants permanently.191
France in the 19th CenturyAs the 19th century dawned there were many more industrial, technical and chemical innovations that affected the art world.192 The traditions of craftsmanship were being replaced by the advent of mass-produced goods. This applied in art to some extent because of the invention and rise in popularity of photography193, which was seen to take the traditional role of portrait painting, and depiction of country landscapes and houses. With photography, a mirror could be held up to the world, which did not require the skill of an artist, and this meant that the art world had to search for a new function.194 The centre of culture in Europe was Paris, where not only the arts flourished but a profusion of scientific inventions were also born. Many great chemists of this era came from France, and many of them discovered or invented new pigments that became of service to the art world.
French ImpressionismDramatic changes occurred in art in Paris that were brought about by a paradigm shift throughout Europe in the way the world was viewed.195 There was a whole myriad of influences: the French Revolution, industrialization, scientific advancement and the rise of common man in the eyes of society, to name only a few. In Paris artists began to look at the world in a completely new way. They left their studios en masse for the first time and actually saw the scenes around them with fresh eyes.2 Artists of the period began to investigate the interplay of light and shadow, movement and colour. They did not paint according to the traditional methods of the academies, but rather tried to create an impression of real life.196 The term ‘impressionism' was adopted for this group of painters; it was initially used by critics as an insult for their lack of technique in painting, but the name stuck and became very appropriate.197
Early artists of this impressionist revolution included Edouard Manet (1832-1883)198,199, Claude Monet (1840-1926)200,201, Pierre Auguste Renoir (1814-1919)202,203 and Camille Pissaro (1830-1903)204. These men painted everyday scenes in a style that suggested form through the use of light and shadow, rather than defining shapes through gradual shading in the accepted style. They were subjected to much criticism and derision at the time and were even rejected from the official Salon exhibition of the Academie. The impressionists banded together to exhibit their work in the Salon des Refusés in 1864205, and many people went along simply to laugh at their efforts. This stormy period in art took about 30 years to pass before the impressionists gained popular acceptance and eventually became wealthy and famous. Indeed the impressionists are still regarded by most people today as ‘real art', which accounts for their amazing popularity.2
The impressionists used colour and light in a new way, and this was reflected to some extent by their choice of pigments.82 In the days prior to impressionism, many artists had chosen wide palettes containing a great number of pigments. The impressionists were more interested in studying the effects of mixing simple colours and lights, so often chose a simple palette of a few base colours. A study of Pissaro's palette showed that it was limited to seven pigments, all squeezed from prepared paint tubes.206 These pigments were: white lead, chrome yellow, vermilion, rose madder, ultramarine, cobalt blue and cobalt violet. This palette shows an absence of green and, more surprisingly, black, which would have been mixed from other colours.
After the acceptance of impressionism, the art world was changed forever, but was left in something of a quandary. Once the problems of imitating vision had been overcome, what was there left to solve? The post-impressionist painters were not content to continue painting as the impressionists, and were left once more to experiment with art.
Expansion of Organic ChemistryAs art expanded in many new directions from the seeds of impressionism, so chemistry expanded from the discovery of coal tar colorants. The discovery of mauveine kick-started chemists throughout Europe to investigate and experiment to produce new colorants from coal tar products.207 In 1858 in France, Verguin (1814-1864) discovered the second coal tar colour, which he named fuchsine, although this was also widely known as magenta.208 The bright-pink colorant was an immediate success and was also produced as a pigment by laking.209
The invention of aniline colours created a new drive to reform industrial practices and adopt a more organized approach to methods of production. The new industrial processes inadvertently led to the discovery of the third aniline colour in 1860.210 Magenta was being manufactured industrially in France using aniline and arsenic acid, and one day a workman in the factory seems to have confused the two chemicals. Instead of adding arsenic acid to the magenta reaction vessel, too much aniline was added by mistake, yielding a blue colour instead of the expected pink.211 Two chemists, Girard and De Laire, happened to observe this unexpected phenomenon, and later patented a method for the synthesis of a new blue colorant, which they simply named aniline blue.212,213 The chemistry of these new dyestuffs was not very well understood, but the dyes themselves were hugely successful.
Dominance of GermanyThe colorant industry at this time was mostly based in Britain and France, but as the 1860s progressed there was a gradual shift of industrial development to Germany and Switzerland, in the formative days of the strong German empire.214 There was also a shift in the approach to chemistry from trial-and-error experimentation to sound chemical theory. These changes occurred partly because of the work of August Kekulé in 1865, who came up with the concept of the six-member carbon ring structure for benzene.215 This discovery gave chemists some insight into the structure of organic molecules. It allowed them to start designing reactions and to expand their knowledge of many other compounds. It was a turning of the tide for organic chemistry and initiated enormous amounts of research work, which still continues in the same vein today.
Alizarin RedChemists began to investigate natural organic products, and some of the first colorants to undergo this treatment were the plant products of madder and indigo, both of which were widely used in the 1800s.187 Madder was a popular pigment and dyestuff for cotton, often known as turkey red.216 The economic importance of madder had long been recognized, and in 1810 Napoleon had signed a proclamation urging the development of madder dyeing for wool.217 In 1820 the Société Industrielle de Mulhouse offered a substantial prize for the best chemical investigation of madder. Sadly, nobody was awarded this prize, but two Parisian chemists, Colin and Robiquet, managed to isolate a red substance from madder.218 This substance was named alizarin and generated a lot of interest from chemists of the time who tried to identify the structure of the mystery compound with the aim of producing a synthetic madder dyestuff.
Madder is actually a mixture of many coloured components, of which alizarin is one of the most highly coloured and easily recognizable.34 Chemists throughout Europe worked on the puzzle of alizarin, but it was eventually a team of German chemists who made the crucial breakthrough and determined the correct structure.219 Their names were Adolf Bayer (1835-1917)220, Carl Graebe (1841-1927) and Carl Lieberman (1842-1914)221; they worked on alizarin from 1865 until 1868 and finally patented a method for its synthesis in December 1868.222 Industrial production of the synthetic madder, alizarin, began in Germany soon afterwards and caused the total demise of the natural madder industry throughout Europe.223
Synthetic IndigoDuring the 1860s and 1870s the vast majority of natural indigo was imported from the British colony of India into London and Liverpool.224 The British had a tight monopoly on the indigo trade in Europe and could keep the colorant at inflated prices, which angered many continental industrialists, and prompted German and Swiss chemists to investigate the synthetic production of indigo. Adolf Bayer had started to research indigo compounds between 1860 and 1865 but had been unable to identify the structure of the blue colouring matter in the plant.225 By 1869 Bayer had succeeded in preparing a synthetic product that was similar to indigo, and was certainly getting near his goal when he was forced to postpone his research.226 The influential chemist Kekulé believed that he was within reach of synthesizing indigo himself, so put a stop to Bayer's research. As it turned out Kekulé's ideas were not correct, and Bayer did not return to his elusive quest for synthetic indigo until 1876. It did not take Bayer long to succeed in his task. By 1880 he had synthesized indigo and filed a patent for it, and by 1883 the correct chemical structure had been determined.227
The industrial production of synthetic indigo did not begin immediately because of the difficulty in finding a production method economical enough to compete with natural indigo. Full-scale manufacture began in 1897, and this prompted competitive price decreases in the natural product.228 Once again indigo became highly politicized as the British government tried to defend its market.229 By the turn of the century the sales of synthetic indigo had overtaken those of the natural product, and the indigo plantations of India were suffering badly due to the crumbling of the British trade monopoly. By 1914 over 90% of all indigo used came from synthetic manufacturing routes.230 During this period laked indigo was very popular as an artist's pigment because it was easily available from two competing sources with the price dropping rapidly.231
The demise of natural indigo and madder marked the end of an era for natural colorants. It was no longer economically viable to grow plants, collect lichens or crush rocks to obtain colorants, so these small cottage industries tended to collapse. Some natural products remained for specialist applications, and some can still be found today, but on the whole they slowly vanished from use.
Beginnings Of Modern ArtArtists of the post-impressionist era were living in times of new invention, discovery and expansion, which influenced the new styles of art produced. There were three artists of the late 19th century of particular note who greatly influenced the schools of modern art that were to follow in the early 20th century.232
The first of these artists was Paul Cézanne (1839-1906)233, who retired from the impressionist art world of Paris to live in the countryside. Cézanne painted scenes from nature but tried to keep the light and suggestion of the impressionists without losing the depth and distance of traditional art.234 He developed a system of building blocks of colours, which later influenced the style of cubism.235
The second artist was Vincent Van Gogh (1853-1890)236, who led a painfully disturbed and lonely life that ended with his suicide at the age of 37. His most famous paintings were all created during three years of intense activity and despair at the end of his life.237 Van Gogh painted in unconventional strokes and splashes of pure colour that make the paintings appear to move and also express the emotions of the painter. He even deliberately distorted images to achieve his aims. He died relatively unrecognized, but later was to have a huge artistic influence on the field of expressionism.238
The third artist was Paul Gauguin (1848-1903)239, a companion and colleague of Van Gogh for a time. Gauguin began to paint late in life after giving up his job as a stockbroker. He became disillusioned with the civilized art of France and eventually went to Tahiti to rediscover simplicity and even barbarity in his art. Gauguin used bold colour schemes and simple forms, often ignoring depth in his paintings.240 Later on the work of Gauguin strongly influenced the idea of a return to primitive art in Europe.
The era of modern art began with the influences of these three painters.241 Artists moved on from and absorbed the lessons of impressionism; they accepted that what we see is always influenced by our perception and by our pre-formed knowledge of what we are seeing. The human visual system and human mind are not perfect, and we can make ‘mistakes' in seeing. The theories of Charles Darwin (published in 1859) about evolution had begun to influence the way in which the people of Europe thought about humanity as a species.242 It was no longer entirely accepted that humans were the perfect creations of a divine being but rather that we had reached our present position by a series of evolutionary steps. Physics, chemistry and mathematics were also expanding in leaps and bounds151, with new and most unexpected discoveries being made on a regular basis. People were questioning their place in the world and even in the universe; they realized that there was a great deal still to discover. The experiments and discoveries of science were intertwined with and paralleled by those of art in the modern era.
An analysis of Cézanne's colour palette has been carried out.243 This showed that a wide range of pigments was being used at the turn of the 19th century. Cézanne's palette was comprised of 17 individual pigments, some of which had been recently discovered.82 The pigments were listed as: cadmium yellow, Naples yellow, chrome yellow, yellow ochre, raw sienna, vermilion, red ochre, burnt sienna, red madder, alizarin crimson lake, burnt lake, emerald green, verona green earth, cobalt blue, ultramarine, Prussian blue and peach stone black. The chemical identity of some of these colours is not clear.
Azo ColoursMore than half of the European colorants industry in the late 19th century was based in Germany239, and many important innovations in pigment technology came from this country. Modern industrial research was also beginning, with collaboration between industrial and academic scientists, and publication of new scientific research journals that facilitated the communication of new ideas. One innovation to benefit from the expansion of communication was the development of azo colorants. Azo colours grew from the discovery of the diazo intermediate by Peter Greiss in 1858, and the first azo dye was synthesized in 1863.244 This dye was a bright yellow colour (Field's yellow) synthesized by Fredrick Field at the company Simpson, Maule and Nicholson. A few of the many azo colours brought to market are mentioned below.
The first azo colours were not well understood chemically, but in 1870 Kekulé and Hidegh actively coupled diazonium salts to engineer azo dyes of known structure.216 The new azo dyes gave very bright, predominantly yellow, orange and red hues, which caused great enthusiasm and excitement. Many of these products were laked to offer an abundance of new pigments for artists, but unfortunately many of these pigments were not tested sufficiently for fastness properties.245 Artists became overwhelmed with bright colours, which often proved unsatisfactory for painting, having poor light fastness, or being fugitive in oils. Colourmen slowly implemented stricter testing procedures for artists' pigments, although many artists had already become disillusioned with the new discoveries, preferring to stick to the tried and tested pigments of antiquity for their paintings.246
True Organic PigmentsA new breakthrough in organic pigments occurred in 1884 when it was discovered that insoluble salts of azo dyes could easily be synthesized to produce true pigments that did not need to be laked onto an insoluble carrier material.247 Prior to this discovery all organic pigments had actually been laked dyes248, so the invention of a ‘true' pigment brought about a whole new way of thinking about pigment synthesis. The dye and pigment industries gradually started to diverge from each other. The very first azo pigment was tartrazine yellow245, patented in 1884 and still in use as an artist's pigment today. Chemists were now able to build molecules with greater understanding, and vast numbers of new azo pigments were rapidly introduced. A whole range of b-napthol azo dyes and pigments was introduced after an initial discovery in 1895, many of which are still in use today, for example toluidine red.
A famous family of azo pigments was introduced in Germany in 1911, known as the Hansa pigments.245 The first colorant of this group was synthesized by Wagner, called Hansa Yellow G. It was a very bright yellow pigment and was the first of many to be produced with great commercial success.
Cadmium ColoursA range of yellow, orange and red inorganic pigments based on the element of cadmium were commercially introduced around the beginning of the 20th century18, although they had been known for several decades beforehand. Yellow cadmium sulphide was actually discovered by Stromeyer in 1817 when he observed a sample of zinc carbonate that formed an oxide that was bright yellow in colour rather that white.249,250 Stromeyer deduced that the colour was due to a new element, which he identified and named cadmium. He suggested that this yellow substance was suitable for use as an artist's pigment, but at the time this was not possible due to the scarcity of cadmium. By the 1840s cadmium was being produced industrially, and a small amount of the yellow pigment became available to artists.251 Winsor and Newton introduced the cadmium yellow to Britain under the name aurora yellow in the Great Exhibition of 1851, held at the Crystal Palace.252 Cadmium sulphide came to be renowned as a bright yellow pigment with very good fastness and stability properties, but was also difficult to obtain and expensive.
In 1921 cadmium lithopones18 were introduced. These were manufactured by precipitation of cadmium sulphide with barium sulphate to give a yellow pigment. Experiments were also carried out with other materials to produce mixed cadmium pigments of varying hue. Cadmium sulphoselenides were introduced providing attractive orange and red shades.59 Mercury and cadmium pigments were also introduced to give other orange and red shades.253 All of the cadmium pigments were very popular with artists for all types of painting and drawing media, and some are known to have been used by Monet, Van Gogh and Matisse.254 Cadmium pigments are still being used today but are gradually being phased out because of concerns over the toxicity of cadmium.
Twentieth Century ArtThe artists of the 20th century had to become pioneers, explorers and inventors. The most successful of these experiments formed a new art genre. One of the first groups in this new art world was expressionism255, which began before the First World War in Germany and was strongly influenced by Van Gogh's work. Expressionism tried to show feelings and emotions by deliberate manipulation of artistic form and style. An early painter of this group was the Norwegian Edvard Munch (1863-1944)256, who painted the famous picture The Scream. In this painting reality is distorted by the use of harsh lines and perspective to make an unsettling image of a screaming figure. Expressionism often upsets people by its refusal to depict pretty, harmonious scenes.257 It concentrated instead on gritty, real life images of suffering, agony and social truth, which took a decidedly political aspect after the First World War.258 The art style was banned by Hitler when the Nazis came to power in 1933, and many of the expressionist artists were exiled or persecuted. Famous artists of this period include Otto Dix (1891-1969)259 and Käthe Kollwitz (1867-1945)260, who produced many bitter, haunting images.261
Colour ClassificationWith the vast amounts of new colorants being produced, the requirement for some type of colorant indexing system was recognized. The German chemists and colour makers were the first to identify this need, and one early classification system was a publication by Schultz and Julius in 1888.262 This publication ran to several editions in the years up to 1914, reflecting the increase in the number of colorant products from 278 to 1001 over this time span.263 At this time the majority of all colorant production was carried out in Germany, and it seemed only natural that any colour classification system would be German in origin, but in 1914 political circumstances changed the balance of technological power in Europe. The First World War (1914-1918) stifled the flow of innovation, chemicals264, colorants and trade with Germany and the need for an English language colour indexing system was recognised as being highly important.265
During the First World War there was a huge expansion of research and manufacture in colorants by the British and also by the Americans266, initially to aid the production of uniforms and equipment for the armed forces but also to develop technology comparable to that held by the Germans. From 1920 the Society of Dyers and Colourists began trying to devise ‘some means or other to systematize the nomenclature of the colours'.263 The first Colour Index was published in 1924266, followed by the second edition in 1956 in which the now well-established system of colorant nomenclature appeared.267 In 1998 an edition designed explicitly for the pigment industry was published.268 The Colour Index is still the only colour classification system that attempts to categorize all known colorants, and is invaluable to anyone with an interest in dyes and pigments. Most recently it has been released on CD-ROM. The development of a comprehensive colorants indexing system allowed chemical producers, dyers, researchers and artists to identify exactly what substances they were using.
Important DiscoveriesEarly in the 20th century two new pigments were discovered that would again revolutionize the colour industry. As often seems to happen, one of these pigments was actually discovered accidentally as an impurity. The pigment in question was blue phthalocyanine269, first reported as a blue impurity by Braun and Tchernaik in 1907, although they failed to recognize the potential of their observation. The real discovery of phthalocyanine occurred at an ICI plant in Scotland in 1928, where a stable, insoluble blue impurity was found in reaction vessels.270 The blue compound was analysed by Linstead at the Imperial College of Science and Technology in London and found to be iron phthalocyanine.271 The structure was identified and a method of synthesis formulated. Eventually the more intense blue copper phthalocyanine was synthesised.272 A viable manufacturing method for the pigment was patented in 1932. ICI began production of its new colorant in 1935 under the trade name of Monastral Fast Blue BS, and later introduced a green halogenated copper phthalocyanine to the range.
The phthalocyanines were the first class of organic colorants to be introduced directly to the market as ‘true' pigments, without initially being developed as dyes or lakes. They were a new class of super pigments with incredibly high performance in terms of tinting strength, fastness and chemical resistance; thus they quickly came to dominate the blue and green pigment markets in all applications. In a very short time they had all but replaced the synthetic indigo lake pigment over which there had been so much political and economic turmoil only 20 years earlier. The phthalocyanines are immensely popular as artists' pigments and are used in nearly all pigment applications today.273 Indeed they are the most widely selling organic pigments at the present time.
The second important pigment to be discovered in the 1920s was white titanium dioxide.59 The white mineral rutile had been known for some time, but it was not until 1795 that German chemist Klaproth identified it as the oxide of a new element, which he named titanium.17,162 Naturally occurring titanium dioxide was not used as a pigment because it was too highly contaminated with iron and a suitable purification method had not been worked out. In the 1920s a suitable method of producing white titanium dioxide pigment was developed, known as the sulphate process.274 Natural titanium minerals are treated with sulphuric acid at about 200 °C to form a sulphate solution, which is then hydrolyzed to form a white precipitate of hydrated titanium dioxide. The precipitate is calcined in a furnace to form the white pigment with the correct properties. Titanium dioxide is nowadays often manufactured by another method called the chloride process and it is the most widely used pigment of all time. It is very safe to use, has the highest hiding power of all the white pigments, has excellent light fastness and is very popular in modern artists' colours, in addition to being very widely used in decorative paints, plastics, printing inks and many other applications.30
Modern ArtThe style of art that was influenced by the work of Cézanne was called cubism and was developed in Paris at the dawn of the 20th century.275,276 It has been described as the most influential style in modern art. Cubism was developed partly by the Spanish painter Pablo Picasso (1881-1973)277,278, and it is concerned with the analysis of form in painting. These painters created familiar objects from flat building blocks of simple units, often using many angles and views to do so. Cubist painters were concerned with form first and subject matter second.279
The cubist style was crucial to the development of a new movement of abstract art. Abstract artists were interested solely in the form of a painting and abolished reliance on subject matter altogether.280 Painters were free to study pure colours and our psychological responses to them. They began by looking at the human visual system and thought processes through experiments in art.281,282 The first abstract painter is considered to be Russian-born Wassily Kandinsky (1866-1944)283,284, who lived and worked in Munich. The scientific experimentation of cubism and abstract art were in some ways combined by artists such as Piet Mondrian (18721944).285,286 He built abstract pictures but out of solid forms, blocks of bright, primary colours and bold outlines, which probed the laws of vision and colour.287
Modern art tried to create new forms and to explore new ideas that had not previously been considered. In order to facilitate this creative process, many artists took a lead from Gaugin's primitive paintings of Tahiti and tried to return to a naive state from which to begin their work. Gaugin's work sparked a cascade of naive, childlike paintings and a great interest in folk art and the art of ‘primitive' cultures from the countries of the European empires.288 Naive artists, unlike the expressionists, were widely supported by both Nazi Germany and later by the Soviet Union. The concepts of naive art were absorbed and developed to found the Dada movement.289 This took the idea of returning to a childlike, primitive state to an extreme by rejecting all aspects of Western culture and conventional art.290 Many Dadaists used new materials such as discarded rubbish and waste paper in order to create their work, and many set out to shock the public out of their bourgeois art tastes.291 A leading Dadaist named Marcel Duchamp (1887-1968) became famous for exhibiting ready-made sculptures, which were commercially produced items, such as in one instance a urinal.292,293 Many of Duchamp's works were interactive with moving parts, and the public was invited to touch and feel the works in galleries. This began a trend for art being incorporated into everyday life, reducing some of the taboos and restrictions associated with attending an art gallery. The public was encouraged to obey their childlike instincts and investigate what they could see.
Being deliberately naive obviously caused problems, because it was not possible for any painter to adopt a primitive viewpoint all of the time or ‘unlearn' all of their knowledge and preconceptions. Naive art and Dada began to become increasingly fantastic and based less in reality.291 Many artists had been strongly impressed by the ideas of Sigmund Freud and investigated the concept that art cannot be created by waking reason. Painters deliberately set out to paint their subconscious thought; these artists became known as the surrealists.294 Perhaps the most famous surrealist painter was Salvador Dali (1904-1989)295, who tried to reproduce a dream world in his work. Dali's paintings are a confused mix of images, which cleverly blend into one another to form new images.296 Some objects in his paintings are illustrated with extraordinary clarity while some are deliberately vague and cannot quite be made out, like memories of a dream.
The American Art SceneThe Second World War was to have a deep impact on the art communities of Europe and on the world perception of art generally.297 Britain and France entered the war in September 1939, and intellectuals from all disciplines began fleeing European countries for the haven of America.258 The Parisian art scene in between the wars had been dominated by the surrealists, cubists and abstract artists, and many of the individuals involved in these scenes went to New York. Artists such as Dali, Max Ernst (1891-1976)298 and Mondrian all took part in this exodus. Only a few of the major artists, including Picasso and Kandinsky, were to remain.
Before the Second World War the American artists of New York had taken great inspiration from the European art schools. Other influence came from the leftist revolution of Mexico (1911-20). In Mexico a great tradition of Socialist mural painting had been created that was sustained by state sponsorship.299 Famous fresco artists such as Diego Rivera (1886-1957)300 and David Siqueiros301 won international acclaim for their socially realistic work and even obtained commissions for large fresco works in America. Siqueiros set up a workshop near Union Square in New York. He introduced many young artists to his experimental painting techniques and to the use of new media such as industrial paints. The American stock market crashed in 1929 causing the great depression, and the artists of the day felt this intensification of social pressures, tending to become very politically minded.302 During the 1930s the Union Square area of New York became a hive of artistic activity reflecting these social issues, and a federal art project was set up. Thousands of artists were involved in this project and were paid a basic subsistence allowance to work and paint. The project generated hundreds of thousands of art works, and many of the young painters involved went on to form the New York art school. Such painters included Stuart Davis302, Jackson Pollock 303, Willem de Kooning 304, Lee Kranser302 and Mark Rothko305, who were all to become very famous during their lifetimes.
The New York SchoolThe New York artists became more heavily influenced by European modern art in the 1930s after the opening of several new art museums in the city.306 New York artists had their first chance to study the works of European art face to face, to view the actual paintings from which they had taken inspiration. Paintings by Picasso and the surrealists provided a particularly strong influence; the flat cubist figures of Picasso are much in evidence in American art of the time. The influence of European art intensified still further with the arrival of the artists themselves after 1939. The surrealist and Dada artists stepped into the New York limelight and brought with them a strong sense of community, which was something lacking amongst the American painters.307 In Paris the art communities had been settled in established areas of the city, with members frequenting certain cafes, taking part in lively discussions and debate. The upheaval to America meant that new meeting places needed to be established and frequently these places became the art galleries. One of the most important galleries was a privately run exhibition area belonging to Peggy Guggenheim308, who called her gallery ‘Art of this Century'. A profusion of small magazines and art-criticism journals also began to appear to give the artists a voice to communicate with each other across the city. These changes due to the exodus from Europe are still in existence to this day.302 The art galleries all over the world are always the focal point for people to meet and discuss art, with most galleries running extensive lecture and information programmes for the public.
The mingling of artistic and political influences caused the emergence of a new art movement that was centred in New York. In 1945 Peggy Guggenheim's gallery308 hosted an exhibition called ‘A Problem for Critics', where the art critics were challenged to identify the new style. The show featured works by many American artists302 including Hans Hofmann, Jackson Pollock, Arshile Gorky and Mark Rothko. These artists collectively became known as the abstract expressionists309, or the New York School, and for the first time American art led the world. The abstract expressionists were a group of individuals who had a great deal in common.310 They generally came from similar cultural and political backgrounds, and were all influenced by European modernism and the surrealists with an interest in the unconscious mind. They all believed strongly in individuality and denied being part of a group at all; they also objected strongly to the term abstract expressionism.
New TechniquesJackson Pollock (1912-56) was a particularly prolific painter of the New York group; he was involved in the New York art scene from his youth and painted in many styles. His mature works, for which he is most famous, were particularly innovative and have greatly influenced many subsequent artists. Pollock created ‘action paintings'311, where he would take huge canvases, place them on the floor and drip, pour or splash the paint across them to make textured images. There was no actual subject matter involved in the paintings but the whole canvas was covered with paint and itself became the subject matter. Pollock redefined our ideas of painting. He often used novel materials in his compositions, including enamel paints, household decorative paints and industrial paints.
The American painter Mark Rothko carried out another novel investigation in art but this time with his use of colour.305 Rothko also had many different styles of painting until he settled on his mature style, which was often called colour field painting, which consisted of using large canvases filled with rectangles of colour painted in many layers to produce shimmering and glowing colour effects. Rothko did not title many of his paintings312 but simply gave them exhibition numbers or names such as ‘Composition in red and black'. The ideas behind these paintings were central to the abstract expressionists.302 It was felt to be important to remove the barriers of the conscious mind to allow art and free thought to come entirely from the subconscious, with a new perspective.
During the explosion of American art there were also a great many new pigments that were introduced by science and industry. The new artists took advantage of these new materials and often used them in interesting forms. The new organic pigments were bright, attractive and had good properties so were quickly adopted by the artists of the New York School.313 Many new painting materials were also developed after the introduction of novel synthetic-polymer systems and other technologies. In addition to the more traditional painting styles of fresco, watercolours, egg tempera, oils and chalks, the modern artists could choose from printing inks, emulsion paints, oil pastels, acrylic paints, coloured pencils, wax crayons, enamel paints, aerosol spray paints, etc. From this large selection of styles modern artists began creating collages or sculptures, and experimenting with art media using just about any material in their work.
Modern PigmentsTwo more classes of organic pigments that have been more recently developed and used as artists' materials deserve specific mention. The first of these are the quinacridone pigments314, which like the phthalocyanines are polycyclic in nature. Quinacridones are very highly coloured, ranging from yellowish-red through to violet hues. They have excellent fastness and resistance properties and have been used in high-quality artists' materials.
Evidence of the quinacridone structure was first uncovered in 1896 but a linear quinacridone suitable for use as a pigment was not synthesized until Liebermann began work in 1935.315 He failed to recognize the potential use of this structure as a pigment, and it was not until 20 years later that any industrial progress was made. In 1955 Struve began investigating commercially viable synthetic routes to quinacridone pigments for the DuPont Company. The pigmentary potential of quinacridones was uncovered once it was realized that the quinacridone structure could exist in several crystal forms.316 The standard quinacridone could be converted to a very stable, highly coloured form, ideal for pigmentary applications. It took several years to perfect a synthesis, and in 1958 a new class of pigments was introduced into the market place.317 A wide range of quinacridone pigments are commercially available, but CI Pigment Violet 19 and CI Pigment Red 122 are two of the most important.
The last group of pigments to be introduced in recent times are the diketopyrrolopyrrole (DPP) pigments.314 These are ranges of organic pigments that are based on a specific type of heterocyclic chromophore discovered after a series of experiments carried out in 1974.318 The unusual heterocyclic compound produced was investigated by Iqbal at Ciba and eventually yielded an entirely new class of colorant, the DPP pigment.319 The exact date of Iqbal's discovery is not known since the work was carried out with great secrecy, but the new pigments were patented in 1983 when a synthetic production route had already been established commercially. Diketopyrrolopyrrole pigments are red and orange in hue and have all-around excellent pigment properties, which makes them desirable despite their high price. They have been used in some good-quality artists' materials and it is likely that their use may increase. Commercially, the most important DPP pigment is CI Pigment Red 254.320
ConclusionsArt is continuing to develop and grow, tackling new ideas and themes. At any one point in history, it is difficult for the observer to evaluate what is and what is not significant in the field of contemporary art. It will be the job of the art historians of the future to analyze the trends of the late 20th century. Nevertheless, this paper has attempted to review the history of pigments in art from cave paintings of 40,000 BC to the art works of today. The progression from primitive man creating paintings with animal fat and crushed earth to the complex industrial synthesis of organic pigments and careful formulation of high-quality artists' materials has been outlined. The developments in art and science through the centuries appear to have been a series of diversifications, expansions and experiments, which have run very much parallel to one another. As the number of art styles has developed, so too has the artists' palette and the variety of painting techniques available. It is hoped that this review has provided an insight into the long history of pigments and art, and also inspired the reader to look at painting in a new light.
Originally titled "A Colour Chemist's History of Western Art", published in Review of Progress in Coloration, Millennium Issue, Vol. 29, 1999, pp 43-64, Society of Dyers and Colourists, Bradford, UK.
Part 1 of this article ran in the January 2004 issue.
References1. Osborne, R. Lights and Pigments; London: John Murray, 1980.
2. Gombrich, E.H. The Story of Art; 15th Ed. London: Phaidon, 1995.
16. Harley, R.D. Artists' Pigments 1600-1835, 2nd Ed.; London: Butterworths, 1982.
17. Paint and Painting London: Tate Gallery Publications, 1982.
18. Feller, R.L. Artists' Pigments; Cambridge: CUP, 1986.
30. Innes, J. Trade Secrets: Classic and Contemporary, Surfaces and Finishes; London: Phoenix, 1995.
34. Grierson, S. The Colour Cauldron; Perth: Grierson, 1989.
41. Ayres, J. The Artists' Craft; London: Phaidon, 1985.
59. Pigment Handbook, Vol. 1, Ed. T.C. Patton; New York: John Wiley, 1973.
82. Birren, F. History of Colour in Painting; New York: Van Nostrand Reinhold, 1965.
151. Partington, J.R. A History of Chemistry; London: Macmillan, 1964.
154. Hope, A.D. The Age of Reason; Carlton, Victoria: Melbourne University Press, 1985.
155. Nicolson, H.G. The Age of Reason 1700-1789; London: Constable 1960.
156. The Works of William Hogarth; London: London Printing and Publishing, 1833.
157. The Dumb Show, Ed. F. Ogee; Oxford: Voltaire Foundation, 1997.
158. 1789: French Art During the Revolution, Ed. A. Wintermute; New York: Colnaghi, 1989.
159. Yates, F.A. The French Academies of the 16th Century; London: University of London, 1947.
160. Olander, W. French Painting and Politics in 1794; New York: Colnaghi, 1989.
161. Held, J.S. 17th and 18th Century Art; New York: Abrams, 1972.
162. Hudson, J. The History of Chemistry; London: Macmillan, 1992.
163. Taylor, F.S. A History of Industrial Chemistry; London: Heinemann, 1957.
164. Milestones in 150 Years of Industrial Chemistry, Ed. P.J.T. Morris, W.A. Campbell and H.L. Roberts; London: Royal Society of Chemistry, 1991.
165. Brown, H. Scientific Organisations of 17th Century France; Baltimore: Williams and Wilkins, 1934.
166. Buchannan, W.D. Toxicity of Arsenic Compounds; Amsterdam: Elsevier, 1962.
167. Williams, G.A. Goya and the Impossible Revolution; London: Allen Lane, 1976.
168. Goya and the Spirit of Enlightenment; Boston: Boston Museum of Fine Arts, 1989.
169. Wilton, A. The Life and Work of J M W Turner; London: Academy Editions, 1979.
170. Brown, D.B. From Turner's Studio; London: Tate Gallery, 1991.
171. Rosenthal, M. Constable; New Haven: Yale University Press, 1983.
172. Parris, L.; Fleming Williams, I.; and Shields, C. Constable; London: Tate Gallery, 1976.
173. Brown, H.E. Zinc Oxide Rediscovered; New York, 1957.
174. Faloon, D.B. Zinc Oxide; New York, 1925.
175. The Aphorisms of Hippocrates (trans. T. Coar); London: Longman, 1822.
176. Jones, W.H.S. Philosophy and Medicine in Ancient Greece; London: John Hopkins Press, 1946.
177. Cocks, E.J.; and Walters, B. A History of the Zinc Smelting Industry in Britain; London: Harrap, 1968.
178. Petit, G. The Manufacture and Comparative Merits of White Lead and Zinc White Paints (trans. D. Grant); London, 1907.
179. Lead Toxicity, Ed. R. Lansdown and W. Yule; London: John Hopkins Press, 1986.
180. Nelson, A. The Versatile Paint Making Properties of Zinc Oxide; New York, 1940.
181. Hofmann, A.W. Ann. Chim. Phys., 3rd Series, 9 (1843) 129.
182. Perkin, W.H. J. Chem. Soc., 69 (1896) 600.
183. Read, J. Sir William Perkin; Oxford: Pergamon, 1956.
184. Jubilee of the Discovery of Mauve and of the Foundation of the Coal Tar Colour Industry by Sir W H Perkin, Ed. R. Meldola, A.G. Green, J.C. Cain; London: Perkin Memorial Committee, 1906.
185. Perkin, W.H. British P 1984 (1856).
186. Leaback, D.H. Chem. Brit., 24 (1988) 787.
187. Travis, A.S. The Rainbow Makers; London: Associated University Press, 1993.
188. Calvert, F.C. Dyeing and Calico Printing 3rd Ed.; Manchester: Palmer and Howe, 1876.
189. Perkin, W.H. Sci. Amer., 95 (1906,) 342.
190. CIiffe, W.H. J.S.D.C., 73 (1957) 313.
191. Morris, L.E. Dyer, 115 (1956) 747.
192. Technological Development and Science in the Industrial Age, Ed. P. Kroes and M. Bakker; London: Kluwer Academic, 1992.
193. Scharf, A. Art and Photography; Harmondsworth: Penguin, 1968.
194. Bruce, G.; and Grundberg, A. After Art: Rethinking 150 Years of Photography; Washington: University of Washington Press, 1994.
195. Boime, A. Art and the French Commune; Princeton: Princeton University Press, 1995.
196. Roos, J.M. Early Impressionism and the French State; Cambridge: CUP
197. Herbert, R.L. Impressionism; New Haven: Yale University Press, 1988.
198. Courthion, P. Edouard Manet; New York: H N Abrams, 1962.
199. Brombert, B.A. Edouard Manet; Boston: Little Brown, 1996.
200. Spate, V. The Colour of Time; London: Thames and Hudson, 1992.
201. Thompson, R. Monet to Matisse; Edinburgh: National Gallery of Scotland, 1994.
202. Renoir, J. Renoir; Paris: Hachette, 1972.
203. Gaunt, W. Renoir, 3rd Ed.; London: Phaidon, 1972.
204. Brettell, R.; and Lloyd, C. A Catalogue of the Drawings by Camille Pissaro in the Ashmolean Museum, Oxford; Oxford: Clarendon Press, 1980.
205. Mainardi, P. The End of the Salon; Cambridge: CUP, 1993.
206. Lane, J.W.; and Steinitz, K. Art News (Dec 1942) 1.
207. Reimann, M. On Aniline and Its Derivatives (trans. W. Crookes); New York: John Wiley, 1868.
208. Sack, E.A. Teintex, 23 (1958) 855.
209. French P 40 635 (1859).
210. Prunier, P. Textile Colourist, 1(1879) 180.
211. Hofmann, A.W. Proc. Royal Soc., 12 (1863) 578.
212. French P 45 826 (1860).
213. Hofmann, A. W. Proc. Royal Soc., 13 (1863) 13.
214. Beer, J.J. The Emergence of the German Dye Industry; London: University of Illinois Press, 1959.
215. Wilcox, D.N. Kekulé and the Dye Industry, Kekulé Centennial, Advances in Chemistry Series; New York: American Chemical Soc., 1966 24.
216. Cliffe, W.H. Turkey Red in Blackley: A chapter in the history of dyeing; Manchester, 1976.
217. Edelstein, S.M. Amer. Dyestuff Rep., 43 (1954) 33.
218. Colin, J.J.; and Robiquet, P. Ann. Chimie Phys., 34 (1827) 225.
219. Hornix, W.J. Proc. 17th Int. Congress of History of Science, Berkeley (1985).
220. Bayer, A. Ann. Chem. Pharmacie, 140 (1866) 295.
221. Graebe, C; and Liebermann, C.; L'alizarine artificielle, trans. W. Prud'homme, Moniteur Scientifique, 3rd Series, 21 (1879) 394.
222. French P 83 557 (1868).
223. Travis, A.S.; Hornix, W.J.; and Bud, R. Brit. J. Hist. Sci., 25 (1992) 5.
224. Travis, A.S.; Hornix, W.J.; and Bud, R. Brit. J. Hist. Sci., 25 (1992) 113.
225. Mathews, J.M. J. Soc. Chem. Ind., 20 (1901) 551.
226. Bayer, A. Ber. Deutschen Chem. Gesellschaft zu Berlin 1 (1868) 17.
227. Adolf von Bayer's gesammelteWerke, (Berlin: Friedrich Vieweg, 1905).
228. Thurow, G.M. Isis, 73 (1982) 363.
229. Perkin, F.M. Nature, 62 (1900) 9.
230. Rawson, C. Report on the Cultivation and Manufacture of Indigo, 2nd Ed.; Calcutta: Baptist Mission Press, 1907.
231. Levinstein, I. J.S. D.C., 27 (1901) 157.
232. Rewald, J. Post-impressionism, 3rd Ed.; New York: Secker and Warburg, 1978.
233. Dagen, P. Cézanne; Paris:Flammarion,1995.
234. R Shiff, Cézanne and the End of Impressionism; Chicago: University of Chicago Press, 1984.
235. The Complete Paintings of Cézanne, Ed. S. Orienti; London: Weidenfeld and Nicholson, 1972.
236. The Complete Van Gogh, Ed. J Hulsker; London: Phaidon, 1980.
237. Stone, I. Lust for Life; London: Mandarin, 1989.
238. Vincent Van Gogh: The Complete Letters, 2nd Ed.; London: Thames and Hudson, 1959.
239. Estienne, C. Gauguin; Paris: Nathan, 1989.
240. Roskill, M. Van Gogh, Gaugin and the Impressionist Circle; London: Thames and Hudson, 1970.
241. Loevgren, S. The Genesis of Modernism; London: Indiana University Press, 1971.
242. Darwin, C. The Autobiography of Charles Darwin, Ed. N. Barlow; London: Collins, 1958.
243. Encyclopaedia Universalis; Paris: Encyclopaedia Universalis, 1935.
244. Hornix, W.J. Proc. 18th Int. Congress of History of Science, Hamburg and Munich (1989).
245. Berrie, B.H.; and Lomax, S.Q. Conservation Res., (1996) 8.
246. ASTM D-1 1036, Standard Practice D 4303 (1994).
247. Boyd, S.N. Mechanisms of the Diazotization and Azo Coupling Reaction, ACS Monograph 127; New York: American Chemical Soc., 1955.
248. Jennison, F.H. The Manufacture of Lake Pigments from Artificial Colours; London, 1900.
249. Allen, E.T.; and Crenshaw, J.L. Amer. J. Sci., 34 (1912) 341.
250. Stromeyer, F. Ann. Phil. (trans. from Annalen der Physik), 14 (1819) 269.
251. Connell, A. Edinburgh New Phil. J., (1840) 392.
252. Technical notes on cadmium and cadmium pigments; London: Cadmium Association, 1978.
253. Curtis, P.J.; and Wright, R.B. J. Oil Col. Chem. Assn., 37 (1954) 26.
254. Engel, B.L. A Study of the Materials and Techniques Used by Vincent Van Gogh; Ohio: Intermuseum Laboratory, Ohio, 1975.
255. Willett, J. Expressionism; London: Weidenfeld and Nicholson, 1970.
256. Prelinger, E. Edvard Munch, Master Printmaker; London: W.W. Norton, 1983.
257. Expressionism: Die Kunstwende, Herausgegcben van Herwarth Walden; Berlin: Sturm, 1918.
258. Lynton, N. Apocalypse and Utopia; London: Fischer Fine Art, 1977.
259. Otto Dix 1891-1969; London Tate Gallery, 1992.
260. Nagel, O. Käthe Ko11witz; Dresden: Verlag der Kunst, 1963.
261. Weinstein, J. The End of Expressionism; Chicago: University of Chicago Press, 1990.
262. Schultz, G.; and Julius, P. Tabellarische Ubersicht der Kunstlichen Organischen Farnstoffe; Germany, 1888.
263. Tordoff, M. The Servant of Colour; Bradford: SDC, 1984.
264. Lefebure, V. The Riddle of the Rhine; London: Collins, 1921.
265. Gilbert, M. The First World War; London: Harper Collins, 1995).
266. Colour Index, 1st Ed.; Bradford: SDC, 1924.
267. Colour Index, 2nd Ed.; Bradford: SDC/AATCC, 1956.
268. Colour Index International, Pigments and Solvent Dyes Ed.; Bradford: SDC, 1998.
269. Geibler, G. The Origins of Colour; Germany: Hoechst, 1980.
270. Miles, F.D. A History of Research in the Nobel Division of ICI; ICI, 1955.
271. McKeown, N.B. Phthalocyanine Materials: Synthesis, Structure and Function; Cambridge: CUP, 1998.
272. Moser, F.H. Phthalocyanine Compounds; London: Chapman and Hall, 1963.
273. Phthalocyanines in Ullmans Encyclopedia of Industrial Chemistry, 5th Ed., Vol . 20, Ed. B. Elvers, S. Hawkins and G. Schulz; Weinheim: VCH, 1992.
274. Titanium: Extraction and Processing, Proc. Symposium of Reactive Metals Committee, Metals and Materials Society (1996).
275. Golding, J. Cubism: A History and an Analysis 1907-1914, 3rd Ed.; London: Faber, 1988.
276. Cooper, D. The Cubist Epoch; London: Phaidon, 1971.
277. Richardson, J.; and McCully, M. A Life of Picasso, Vol. 1: 1881-1906; London: Cape, 1991.
278. Warncke, C.P.; and Walther, I.F. Pablo Picasso: 1881-1973; Köln: Benedikt Taschen Verlag, 1993.
279. Apollinaire, G. The Cubist Painters: Aesthetic Meditations; New York: George Wittenborn, 1970.
280. Briony, F. On Abstract Art; New Haven: Yale University Press, 1997.
281. Abstraction: Towards a New Art; London: Tate Gallery Publications, 1980.
282. Seuphor, M. Abstract Painting; London: Prentice Hall, 1962.
283. Hahl-Koch, J. Kandinsky; London: Thames and Hudson, 1993.
284. Long, R.C.W. Kandinsky: The Development of an Abstract Style; Oxford: Clarendon, 1980.
285. Poggi, C. In Defiance of Painting: Cubism, Futurism and the Invention of Collage; New Haven: Yale University Press, 1992.
286. Milner, J. Mondrian; London: Phaidon, 1992.
287. Blotkamp, C. Mondrian: The Art of Destruction; London: Reaktion, 1994.
288. Sylvester, D. Modern Art: From Fauvism to Abstract Expressionism; New York: Grolier, 1965.
289. Richter, H. Dada: Art and Anti-Art; London: Thames and Hudson, 1965.
290. Greenberg, A.C. Artists and Revolution: Dada and the Bauhaus 1917-1925; Ann Arbor, Mi.: UMI Research Press, 1979.
291. Short, R. Dada and Surrealism; London: Octopus, 1980.
292. Ramirez, J.A. Duchamp: Love and Death; London: Reaktion,1998.
293. The almost complete works of Marcel Duchamp (catalogue of exhibition at the Tate Gallery, 18 June-31 July 1966) (London: Arts Council of Great Britain, 1966).
294. Gaunt, W. The Surrealists; New York: Putnam, 1972.
295. Soby, J.T. Salvador Dali; New York: Museum of Modern Art, 1941.
296. Ades, D. Dali; London: Thames and Hudson, 1982.
297. Seddon, R. A Hand Uplifted; London: Mullet 1963.
298. Max Ernst: A Retrospective, Ed. W. Spies; London: Tate Gallery Publications, 1991.
299. Goldman, S.M. Dimensions of the Americas: Art and Social Change in Latin America and the United States; Chicago: University of Chicago Press, 1994.
300. Marnham, P. Dreaming With His Eyes Open: A Life of Diego Rivera; London: Bloomsbury, 1998.
301. Rochfort, D. Mexican Muralists: Orozco, Rivera, Siqueiros; London: Laurance King, 1993.
302. Fineberg, J. Art Since 1940: Strategies of Being; New York: Harry N. Abrams, 1995.
303. Landau, E.G. Jackson Pollock; London: Thames and Hudson, 1989.
304. Pratherand, M. Willem de Kooning: Paintings; New Haven: Yale University Press, 1994.
305. Mark Rothko: 1903-1970; London: Tate Gallery, 1987.
306. Tuchruan, M. The New York School: Abstract Expressionism in the 40s and 50s; London: Thames and Hudson, 1971.
307. New York Dada: Exhibition Catalogue; New York: Prester, 1973.
308. Art of this century, Ed. P. Guggenheim; New York: Art of this Century, 1942.
309. Hobbs, R.C. and Levin, G. Abstract Expressionism: The Formative Years; Ithaca: Cornell University Press, 1981.
310. Anfam, D. Abstract Expressionism; London: Thames and Hudson, 1990.
311. Jackson Pollock: 1912-1956; New York: Museum of Modern Art, 1958.
312. Mark Rothko: The Works on Canvas: A Catalogue; New Haven: Yale University Press, 1998.
313. Colorants and Auxiliaries, Vol. 1, Ed. J. Shore; Bradford: SDC, 1990.
314. Herbst, W. and Hunger, K. Industrial Organic Pigments: Production, Properties, Applications, 2nd Ed.; Weinheim: VCH, 1997.
315. Liebermann, H. Ann., 518 (1935) 245.
316. Reeve, T.B.; and Botti, E.C. DuPont Off. Digest, 31 (1958) 991.
317. DuPont, USP 2 281 529 (1958).
318. Farnum, D.G. et al., Tetrahedron Lett., 29 (1974) 2549.
319. Iqbal, A. et. al., J. Coatings Technol., 60 (1988) 37.
320. Ciba-Geigy, USP 4 415 685 (1983).