3 ideas
Cennini lays out roughly thirteen years of training in sequence: about a year drawing on a prepared panel, then about six years grinding colors, boiling size, laying grounds, and gilding, and only then about six years of actual painting. The apprentice masters the materials and the invisible preparatory labor before being trusted with visible, expressive work, so later mastery rests on a deep grasp of how the medium behaves.
Cennini tells the beginner to pick the single best master available and copy that master's manner steadily. He warns that sampling one master today and another tomorrow leaves you with no coherent style and makes you capricious. A borrowed manner absorbed consistently first becomes the foundation from which a personal style later grows, and the beginner should draw from nature above all.
Cennini treats a color's final quality as the product of preparation labor, not only of the raw mineral. Vermilion ground with water every day for twenty years would only grow better and more perfect. Ultramarine must be pulled from lapis lazuli by kneading a waxy dough in lye so the purest blue separates from the grey residue, so the same stone yields grades of very different value.