This painting method is actually a much more simplified version of the original affresco technique. The main difference is that one paints on dry plaster and can therefore develop all kinds of combinations and experimental practices. Nevertheless, one basic rule remains and that is the good condition of the wall, which must be completly free from moisture, dust and dirt. Old plaster coats must be examined for their firmness and removed in case of blown plaster.
The best white colour for secco technique is lime, which, after beeing dried and powdered several times, is mixed with tempera medium or casein. Casein is in fact one of the best mediums to prepare pigments for secco painting. Mixed together with fresh lime, it gives a protective, waterproof combination. The pigments are ground with a small quantity of water and then used with a much diluted casein, in a proportion of 4:1. As with the tempera technique, it’s best to prepare colours fresh every day and avoid the usual trade products. Even though much easier to work, a composition done a la secco must be executed rather quickly and in no more than 3 sessions. The aim is to avoid too much colour layers that may eventually crack.
Another useful medium for this technique is the egg yolk. Combined with lime it gives a very hard and lasting painting material. As before, pigments are mixed with a little water and then with the yolk (1:1).
The general rule of the buon fresco is valid here also : it is best to paint from light to dark and in large, unified colour areas that will not break up visually the general effect.
On dry plaster it is also possible to use the encaustic technique (hot wax), as it was in use in the antiquity, or a more simple wax-soap emulsion. The latter can be thinned with water and has a very fine mat final effect. If it is rubbed with a clean cloth it takes on a glossy effect.