FIFTY SHADES OF CHEMISTRY AND THEIR APPLICATION IN ART
There has always been a very strong link between chemistry and art. The grinding of the pigments, the use of dispersants and the appropriate choice of the surfaces on which the color lays, are a clear example of this tight relationship. Chemistry, in fact, has always been very important not only to promote the evolution of art, but also for the maintenance of cultural heritage, allowing to protect it from the action of chemical and physical agents and to restore it when damaged.
WHEN EVERYTHING STARTED….
This close link between chemistry and art has evolved over the years. The first traces of use of mineral pigments date back to the Paleolithic (300.000-10.000 B.C.). Archaeological excavations in Zambia have revealed some pigments preserved in a niche, probably used as a warehouse, in the caves of Twin River.
These mainly included iron oxide (red), iron oxide hydrate (yellow) and coal (black) and were probably destined to body painting. Only later, thanks to a wider dissemination of communication and commerce, more rare minerals began to be used. The Neolithic was not very innovative from this point of view, but in this period was introduced the use of white colour, which was obtained from domestic animals bones that were dried and heated at high temperatures.
Egyptian civilization, by contrast, was more revolutionary. The Egyptians, in fact, discovered copper minerals such as malachite and azurite, lead ores, tin ores, chalk, many rare coloured minerals, stibite, native iron, cinnabar, natron and lime.
Furthermore, the considerable knowledge of alchemy they had, led to the use of pigments such as Egyptian blue (a mixture of copper silicate and calcium, which was obtained by fusing white sand, gypsum and malachite), Egyptian yellow (produced by reacting an antimony derivative with a lead salt or a corresponding oxide in high-temperature ovens) and white lead. This last pigment was used for thousands of years until the second half of '800. More scientifically, it can be defined as lead hydroxycarbonate and its use was prohibited since 1921, due to its high toxicity.
ALCHEMY AND ART
Alchemy had a great development also in Greek and Roman civilizations, which played a very important role in promoting and transmitting the empirical knowledge accumulated over time.
To the Phoenicians, instead, can be attributed fabric dyeing. Shades of red, such as madder or kermes, were the most utilized colours in dyeing techniques and they were obtained from vegetable or animal extracts. Alizarin, for example, was extracted from the roots of Rubia Tinctorum; Kermes was obtained by an insect (Kermes Vermilio) that lived on oaks; whereas purple was extracted from a mollusk (Murex Common).
Some of these dyes were also used during the middle Ages, when the oil technique started to become popular. To fix the colour to the fabrics, the dyes were anchored on alum particles (sulfate hydrates of aluminum and potassium), which adhered firmly to the textile fibers; this technique is also known as “etching”. Alum also allowed lighting up the colour, making it brighter and stronger.
With the decline of the Roman Empire and the beginning of the middle Ages, the known alchemical techniques did not go lost, but were collected and developed by the Arabs, which integrated them with the knowledge from China and India. The most famous alchemist of the time was known as the Geber and was born in 722 A.D. To Geber and its school, was attributed the discovery of important substances such as concentrated acetic acid, hydrochloric acid, sulfuric acid, nitric acid, caustic soda and aqua regia.
Aqua regia was one of the rare mixtures able to dissolve gold and for years it fueled the desire of alchemists to transform the substances into gold and vice versa.
The middle Ages brought to the discovery of new pigments (especially shades of blue) and lacquers, which were obtained by adsorbing the dye on white solid particles (for example alumina).
THE DISCOVERY OF OIL PAINTING
Subsequently, during the XV Century, oil painting was introduced. This technique adopted for the first time as a dispersing medium for the color, poppy oil, walnut oil or flax oil, instead of yolk and albumen, which were used for tempera paint, technique that was gradually applied less and less. Compared to tempera paint, the mixed with oil colours showed several advantages, since the oil protected the pigments from the attack of external agents and slowed degradation.
New pigments were then introduced in ‘600, century in which, thanks to the colonial empires, some prominent pigments reached Europe. These included:
- Lacquer Kermes (cochineal carminic acid, a plant pest), imported from Mexico
- Indian yellow (magnesium salt of euxantico); probably the first fluorescent yellow
- Gamboge (intense golden yellow), extracted from South-East Asia plants
- Kassel, a black-brown pigment extracted from peat.
TOWARDS MODERN ART….
With the progress of chemistry between the ‘700 and ‘900, many new compounds were synthesized and enriched the palette of many painters due to a significant reduction of costs compared to the past. Another important novelty was the introduction, in 1840, of tin tubes with ready for use colours (i.e. pigments already mixed with linseed oil), whereas in the past each artist had to prepare the colours at time of use.
Numerous new organic pigments were introduced, especially between 1930 and 1940, with an estimate of up to about 600 pigments in the late '900.
It is interesting to note that the painters were not aware of the toxicity of some of the chemicals they used as colours. For example, it was hypothesized that Cezanne, who loved emerald obtained from acetoarsenite copper, contracted diabetes because of the arsenic contained in the colour he used. The same pigment together with lead chromate yellow pigments were thought to be responsible for the aggravation of Van Gogh’s neurological problems and that a similar poisoning was responsible for Monet’s blindness. The use of pigments containing toxic heavy metals, such as mercury, arsenic, lead, cadmium and chromium may also have caused Renoir’s rheumatoid arthritis and Klee’s skin disease. However, the toxicity of these pigments was recognized only from the ‘900.
New synthetic pigments enriched the Nineteenth Century:
Phthalocyanines, which became indispensable for brilliant colors
Quinacridones, red and magenta
Azopigments, yellow, orange and red
Diketopirrols, orange, red and scarlet, as an alternative to cadmium-based pigments
Anthraquinones, several shades of red.
These pigments, compared to natural pigments such as carotene, were much more stable and lasting in time. Moreover, their chemical structure could be modified, changing in this way their properties.
In conclusion, there has always been a strong link between chemistry and art, which over the centuries has evolved, giving a great contribution to art. Artists may therefore be considered a bit chemists and, vice versa, chemists a bit artists.
“Alchimie nell’arte”, Adriano Zecchina
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