Do you know about cadmium paints? Do you think they have something in common with metal? What is their chemical composition? Why are these dyes so popular with painters of the past and present? In all this, we propose to sort it out together. We will get acquainted with yellow cadmium and its properties.
Natural cadmium
Let us first deal with the basics. Cadmium, as a metal, resembles zinc in its properties. They are adjacent to each other in the thickness of zinc ore. Pure cadmium was obtained relatively recently - in 1817.
In nature, we can find sulfur compounds of this substance in the form of greenokite (the name of the mineral). Interestingly, in its properties, it coincides with the characteristics of yellow cadmium, so popular among painters. Greenokit is distinguished by the most beautiful shades of the tonal palette - from sunny to brown. But, alas, it is so rare in nature that there is no question of any of its practical application.
Artificial Cadmium and Painting
But the sulfur compounds of yellow cadmium are obtained artificially. The first such experiment was made in 1829 by tester Melandry. This year was the starting point for the use of orange and yellow cadmium in art.
Thus, the entire palette of cadmium paints will differ in the content of artificially obtained sulfur compounds. Artists appreciate this dye for its saturation, intensity and beauty of color, strength (excluding lemon shades).
These paints are suitable for all areas of art. But masters, as a rule, prefer the color of yellow cadmium precisely in painting. Incidentally, dye was created for her by the inventor himself. The substance is completely non-toxic, has the ability to well cover the base for the picture.
The chemical composition of the coloring material
And now to the essence of yellow cadmium (medium, dark and light), that is, to its chemical composition.
In the first experiments with sulfur compounds of cadmium, the researchers assumed that one molecule of such a paint consists of five parts of sulfur, which are only one part of cadmium. But further experiments provided completely different, but quite interesting conclusions: only one compound of sulfur and cadmium is observed. And in its composition both elements are included in almost equal proportions.
The second incorrect preliminary statement: different tones of cadmium sulfide are achieved due to the variety of structures of paint molecules. Further research has refuted this. The differences between yellow cadmium (light, dark, medium, orange) are based not on the difference in chemical structures, but on the unequal physical characteristics of the molecules.
Artists can see this in a practical example. The intensity of the dye directly depends on the grain size of cadmium sulfide. The density of the substance used has a great influence. The absorbing and refracting features of paints in relation to the rays of sunlight depend on this.
Paint production
How to get yellow cadmium - dark, light and medium? Today, production is carried out according to two methods:
- Dry way. This is the calcination of cadmium compounds in crucibles with sulfur. The method is inconvenient in that it allows you to get only one shade of paint - medium.
- Wet way. This is the precipitation of cadmium salts with hydrogen sulfide. Initially, this effect allows you to get a bright lemon dye. But this is only the start of the process. With further exposure to the substance of hydrogen sulfide, the shade begins to darken until a final one is formed - saturated, almost orange.
We note an important property of paints that are produced by the wet method: all shades of such yellow cadmium acquire the same color upon heating as the dye obtained by the dry method. How does a beautiful orange tone come about? To get it, cadmium is subjected to shock, pressing, prolonged friction.
We will also reveal such a concept as “glaze paint”. This refers to a substance that is obtained by precipitation of cadmium salts with sodium sulfide. Such a dye will be devoid of opacity. The reason is the high content of free sulfur in the substance. Its presence adversely affects the quality of mixing paints.
In order to get high-quality material for creativity at the output, it is necessary to use cadmium sulfide with the following characteristics in production:
- cadmium - 77.8%;
- sulfur - 22.19%.
Features of light shades
We can judge by what was written above that technically pure cadmium sulfide is not able to give a bright lemon hue, which is so appreciated by painters. Therefore, we can assume that the chemical composition of such yellow cadmium is chemically altered.
Lemon yellow shades contain cadmium carbonate and oxalate in addition to sulfur dioxide. It was originally assumed that such additives give the dye greater strength. But this is not so. They only allow you to easily get an unusual bright lemon color during the production process.
Modern studies and observations show that light yellow cadmium has an average opacity on oil. Requires its content in the range of 30-40%. It dries much slower than traditional mid and dark tones.
Features yellow and orange shades
This is not to say that all orange and yellow shades of paint will equally superior to lemon in strength. Of great importance here is the production technology, the composition of the substance, the purity of the components used. In terms of strength, medium and dark yellow cadmium will also differ significantly.
As for their combination with other shades, the mixtures are quite good, persistent. Exceptions are only the following colors:
- copper green;
- Ivory;
- ocher
- black grape;
- ultramarine;
- cobalt purple.
It is worth noting that the strength of the connection also depends on the grade of yellow cadmium itself.
So we got acquainted with the paint, which for several centuries remains a favorite in the painter's palette. Yellow cadmium is presented in three varieties - bright lemon, medium, orange. Each of them has its own chemical and physical properties.