Yellow cadmium for oil painting: properties and obtaining paints

2024 Author: Leah Sherlock | [email protected]. Last modified: 2023-12-17 05:25

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 past and present? We propose to deal with all this together. Let's get acquainted with yellow cadmium and its properties.

Natural cadmium

Let's get the basics out of the way first. As a metal, cadmium resembles zinc in its properties. They are adjacent to each other in the thickness of zinc ore. In its pure form, cadmium was obtained relatively recently - in 1817.

In nature, we can find sulfur compounds of this substance in the form of greenockite (the name of the mineral). Interestingly, in its properties it coincides with the characteristics of yellow cadmium, so popular with painters. Greenockite 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 practical application of it.

Artificial cadmium and painting

But the sulfur compounds of yellow cadmium are obtained artificially. The first such experience wasproduced in 1829 by the tester Melandri. This year was the start for the use of orange and yellow cadmium in art.

Thus, the entire palette of cadmium paints will differ in the content of an artificially obtained sulfur compound. Artists appreciate this dye for its saturation, intensity and beauty of color, strength (with the exception of lemon shades).

These paints are suitable for all areas of art. But masters, as a rule, prefer the color of yellow cadmium in painting. For her, by the way, the dye was created by the inventor himself. The substance is completely non-toxic, has the ability to cover the base for the picture well.

Chemical composition of 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 cadmium sulfide compounds, the researchers assumed that one molecule of such a paint consists of five parts of sulfur, accounting for only one part of cadmium. But further experiments provided completely different, but rather curious conclusions: only one compound of sulfur and cadmium is observed. And its composition includes both elements in almost equal proportions.

Second wrong preliminary statement: different tones of cadmium sulfide are achieved due to the variety of structures of paint molecules. Further research disproved this. The differences between cadmium yellow (light, dark, medium, orange) are not based on the difference in chemical structures, but onunequal physical characteristics of molecules.

Artists can see this with a practical example. The intensity of the dye directly depends on the grain size of cadmium sulfide. The density of the substance used also has a great influence. The absorbing and refractive properties of colors in relation to the rays of sunlight depend on this.

Paint production

How is cadmium yellow obtained - dark, light and medium? To date, 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 because it allows you to get only one shade of paint - medium.
• Wet way. This is the precipitation of cadmium s alts with hydrogen sulfide. Initially, this effect allows you to get a bright lemon paint. But this is just the start of the process. With further exposure to hydrogen sulfide, the shade begins to darken until the final one is formed - saturated, almost orange.

We note an important property of paints that are made by the wet method: all shades of such yellow cadmium acquire the same color when heated as the dye obtained by the dry method. How do you get a beautiful orange tone? To get it, cadmium is subjected to impact, pressing, prolonged friction.

Let's reveal such a thing as "glazing paint". This refers to a substance that is obtained by precipitation of cadmium s alts with sodium sulfide. Such a dye will be deprived of hiding power. Blamearound the high content of free sulfur in the substance. Its presence has an extremely negative effect on the quality of mixing paints.

In order to obtain high-quality material for creativity, cadmium sulfide with the following characteristics must be used in production:

• cadmium - 77.8%;
• sulfur - 22, 19%.

Features of light shades

We can judge from the above that technically pure cadmium sulfide is not capable of producing a bright lemon hue, so appreciated by painters. Therefore, it can be assumed that the chemical composition of such yellow cadmium is chemically altered.

Lemon yellow shades contain cadmium carbonate and cadmium oxalate, in addition to sulphurous. Initially, it was assumed that such additives give the dye greater strength. But it's not. They only make it easy to obtain an unusual bright lemon color during the production process.

Modern research and observations show that light yellow cadmium has medium hiding power on oil. Requires its content in the range of 30-40%. Dries much slower than traditional mediums and darks.

Features of yellow and orange shades

It cannot be said that all orange and yellow shades of paint will equally surpass lemon ones 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 alsovary significantly.

As for their combination with other shades, the mixtures are quite good, persistent. The only exceptions will be the following paints:

• copper green;
• ivory;
• ochre;
• black grape;
• ultramarine;
• cob alt purple.

It is worth noting that the strength of the bond also depends on the grade of cadmium yellow itself.

So we got acquainted with paint, which for several centuries has remained 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.