The use of symbols in paintings from the Renaissance to the start of the nineteenth century, with van Eyck, Rubens, Girodet, and others.
In the Renaissance, while oil painting was still catching on, many of the greatest masterpieces were painted in egg tempera. How, and to what effect?
The standard blue pigment for the Renaissance and on, until about 1710, it was used in many Old Masters before disappearing by 1800.
A beautiful, intense green used by the van Eycks, Tintoretto, Domenichino, and Renoir, it was never popular in oil paints, and quietly died out.