Preparation of Egg Tempera
I buy pigments in powder form from L. Cornelissen & Son by the British Museum. The pigments are usually ground earths, or derived from bone, such as 'Bone Black'. Cochineal beetle shells are ground to make crimson. Famously the semi precious stone lapis lazuli is powered for the pigment 'Ultra Matinee Blue'.
Back in the studio, using a glass muller I grind the power down further by slowly adding water. The pigment is then stored in a jar. Egg yolk is used as the 'binding medium' - the oldest painting medium known. I only mix a small amount at a time of the require pigment and paint quickly, applying a very thin, transparent layers. This is necessary as the egg yolk dries within minutes.