The guide Iconography and Meditation, Icon Painting and their Secret Technique, describes the application of egg tempera as ‘million year old’ stone, finely ground into powder and suspended in an egg/water emulsion.
The sandy particles settle on the flat surface, finding their own rest and natural condition. We use ground stone from all around the world, minerals, metals and oxides, that each has their own integrity and behavior as they dry.
Old iconographers 1,500 years ago used a limited pallet of earth pigments for Painting Egg Tempera. The various schools of icon painters jumped for joy when a traveling merchant would stroll into town. A bag a new earth pigments would be like thanksgiving arriving at the door. They may have brought earth pigments from far way.
In our world, we go to a store and purchase more than we need. We often buy earth pigments, colors we want to try but discover they are useless. I suggest you begin with a few colors, perhaps 12 earth pigments you find easy to work with and build on them.
My book Iconography and Meditation Icon Painting and their Secret Technique gives you an overview on the spiritual understanding of what the icon painting process reveals. The icon book will help you start painting your first icon and lead you deeper into the discipline as a meditation.