Natural mineral pigments

To date, all pigments are divided into two main groups: organic and inorganic pigments. Organic pigments include dyes consisting of hydrocarbon compounds of plant or animal origin or obtained by synthesis from hydrocarbon raw materials (coal, oil, gas). Inorganic pigments include dyes obtained from rocks or individual minerals, as well as metal oxides and their salts obtained artificially. In turn, both organic and inorganic pigments are divided into pigments of natural origin and synthetic. For example, organic pigments of natural origin include natural crapple varnish obtained from the root of madder dye, Indian yellow, indigo, cochineal and many others. Organic pigments of artificial origin include carbon black, green phthalocyanine, ……… Pigments obtained from rocks and minerals belong to the group of pigments of natural origin (ocher, sienna, umber, colored earth, glauconite, hematite, cinnabar, etc.). Among synthetic pigments of inorganic origin, a large group of cadmium compounds, cobalt, lead, titanium and antimony white, chromium oxide and many other compounds of lead, molybdenum, chromium, tin, zinc, manganese and iron can be distinguished. It should be noted that any classification is, to a certain extent, schematic in nature and is not able to reflect the entire variety of manifestations of the object under study. So in the field of pigments, we often observe the duality of classification features and certain difficulties in attributing one or another substance to a certain class of pigments. For example, many organic pigments of natural origin are obtained by planting a coloring organic substance on an inorganic substrate (the same crappe varnish or Indian yellow). And in recent decades, there has been an increase in the tendency to tint the inorganic substrate with synthetic organic pigments or dyes in order to obtain an imitation of one or another traditional pigment. Often, on a tube or a can of paint with a familiar name, we can find a postscript in small print - “imitation”. But this is an extreme case, which does not apply to the essence of our work, it is rather a matter of technology and economics. In this article, we will focus on pigments of natural origin, both organic and inorganic, since it is these pigments that form the basis of the palette of traditional painting techniques, proven over thousands of years of human history and proven to be reliable in the unfading works of ancient masters, from cave paintings of primitive man to creations. our contemporaries. However, we do not want to belittle the merits of pigments of artificial origin. Many of them are successfully used for the production of art materials and their properties are not inferior to natural pigments. Once, in a conversation with A. N. Ovchinnikov, Adolf Nikolayevich remarked in the form of a joke that if the ancient masters had known chromium oxide, they would certainly have used it in their works. In this regard, I would like to say a few words about the use of synthetic pigments by ancient masters. At all times, painters sought to obtain beautiful, expressive and reliable coloring substances and at the same time were not limited only to what nature gives them. This is how the ancient Egyptians learned how to synthesize amazingly beautiful blue paint - Egyptian blue or Alexandrian frit, and paints obtained from plants were known long before the birth of Christ. But the real flourishing in the production of synthetic pigments is associated with the work of Western European alchemists in the Early Middle Ages. In their quest to obtain noble metals artificially, they simultaneously discovered new substances and materials, among which were pigments. Some of them have not been widely used and have not passed the test of time, but others have taken quite a worthy place in the painter's palette. For example, it is known that the first samples of Neapolitan yellow were found on the slopes of Vesuvius and were a natural antimony-lead compound. Although its reserves were limited and were quickly exhausted. But this compound was obtained in the laboratory of an obscure medieval alchemist, according to whose recipe Neapolitan yellow is still produced today. In the Middle Ages, methods were found for producing white lead, masscott, lead-tin, artificial cinnabar, etc. The long history of the use of these pigments for artistic purposes gives us the right to put them on a par with natural materials in many respects. Pigments obtained according to the recipes of ancient masters can be distinguished into a separate group called "historical pigments", thereby emphasizing their important place in the overall palette of modern art materials.

But let's get back to the topic of our article devoted to natural inorganic (or as they are also called mineral) pigments. According to the definition of Yu. A. Rozanov, mineral pigments are understood as colored rocks and minerals, i.e. both monofractions of minerals and a natural aggregate of minerals, called in geology a rock, can be used as a pigment. Examples of the latter are colored clays, coals and carbonaceous shales, limestones and dolmites. It should be clarified that a mineral is called colored, which gives a color line when scratched. Thus, for example, an emerald or ruby, famous for its magnificent colors, is colorless when ground and, therefore, cannot be used as a pigment. On the other hand, not every mineral that gives a color line can serve as a pigment. First of all, this concerns rare and not noticeable accumulations of minerals in nature. For example, the mineral greenockite, which is a natural yellow-orange cadmium sulfide. The mineral is very rare, but its remarkable coloration prompted chemists to synthesize a similar compound, which is still used as a pigment. Minerals from the so-called group of uranium mica can serve as an example of another kind. These are very beautiful brightly colored minerals of yellow, green and red colors, due to their high radioactivity, they are not suitable for the production of pigments. As a result, the aforementioned restrictions on the use of a mineral as a pigment have singled out a relatively small group of minerals and rocks that are practically used in painting. Their total number does not exceed fifty, and the number of the most commonly used ones is usually 20-25 of their varieties. The currently available classifications of mineral paint raw materials cover a rather narrow range of pigments used by industry and do not meet the needs of painters and restorers working in the tempera technique based on natural mineral pigments. So, the pigment raw materials according to geological and mineralogical features, chemical composition and technological properties are divided into several types: clay, iron oxide, siliceous, carbonaceous, phosphate, carbonate and sulfate. The most common pigments are clay and iron oxide types, and it is these pigments that are the main focus of both researchers and manufacturers of mineral pigments.

A.V. Grigoriev