At first the available colors are ground on a stone slab, by either rubbing or grinding, to bring them into a powder form. Some artists will use mortar and pestle of a very hard quality stone, then that color is dissolved in water along with some gum and then filtered.
The filtration process is continued till the color becomes totally earth or sand free. At which time the water is removed and the color is dried and kept in the form of balls. When required, the desired color along with some dry gum is dissolved slowly in water with the help of a finger or thumb so that the color will be ready to use.
By dissolution, the color starts getting thicker and begins to gain the required consistency of a paste, then pressure is required to be applied. The color will get well mixed from the strength that is applied at this time. This process is termed as tempering, which is the process known as Tempera. If the color is once allowed to get dry and then made thinner as per requirement by adding water, then it will give the artist better results.
The colors used in painting can be divided into four main groups, which are earth or mineral colors, vegetable colors, oxide colors, and metal colors. Colors that are available in the form of stones will fall into the category of earth or mineral colors. For example consider the color black, which is a basic color. A sand lamp is placed over a lighted lamp till a black soot or lamp black, known as kajal, is obtained from it.
Babul gum, Acacia resin and water are added to this kajal, then ground slowly with the first finger till it gets tempered to obtain a fine black color. Black ink is also prepared at Jaipur in this manner. The only difference in the writing ink and black color is that the former has more gum than the latter. The color prepared from the soot of a lamp using mustard oil, though being a watercolor, is unassailable by water after it has dried on the paper.
The colors obtained from different parts of trees or plants fall under the category of vegetable colors. For example, the preparation of red colors from the bark of the peepal tree, which is immersed in water and cleaned, then it is crushed along with borax suhaga and heated in an iron pot. This makes the color come out, which can be preserved in cotton wool or it can be kept secure by concentrating in tablet form.
Oxide or chemical colors are obtained by burning, pulverizing, or mixing various materials by chemical process. For example, consider the emperor of all green colors, the Jangal color. Approximately nine hundred grams of copper powder and eighteen hundred grams of Nausadar, or sal ammoniae, both should be kept in a copper pot. Lime juice should be squeezed into it till it is two inches above the medicine, or material in the pot. The mouth of the pot should now be covered by a cloth, then it should be kept forty days in that condition. This material should then be ground in the same juice, then dried up in shade, which will result in a good quality Jangal. Whenever required, it should be mixed with glue to use, because gum does not suit this color.
Metal colors are fine powders of gold, silver, and lead that have been used in paintings as well as mica pieces. It can be ground and applied like other colors, but gold leaves are used in two ways. In the first process, the leaves are pasted directly, with a mixture of glue and sugar that is applied at the required spot in the required size. Then the gold leaves are pasted, moistening it with mouth in between. Minute and fine work is done by means of golden or silver powder specially prepared, which is called Hilkari in local dialect.
To prepare Hilkari, a thick paste of gum, glue or honey is applied on a metal plate. The gold leaf is pasted over it and it is rubbed with the help of four fingers or the palm in a rotating manner. By doing so, the leaves turn into a fine powder. It is necessary that the paste on the plate should be thick. If the paste is thin, then the gold leaves would turn into balls. This finely ground gold powder is transferred to a tumbler gradually and simultaneously with water. In the end the whole glass is filled with water and the Hilkari, which is left as such for twenty four hours and then the water is drained off. The gold or silver settles at the bottom, but when required, it may be applied after mixing a small quantity of gum. On rubbing agate stone over it, that part begins to shine like gold. With Hilkari the quantity of gum should not be much otherwise the gold would not shine.