Short answers, pulled from the story.
The oldest known oil paintings were carved into the rock walls of Bamiyan, Afghanistan, by Buddhist artists around the 7th century AD. These murals utilized a sophisticated binding of pigments in drying oil that remained unknown to European painters for nearly nine hundred years.
European artists began using oil paint instead of egg tempera during the 15th century with the Early Netherlandish painters Jan van Eyck and Robert Campin. By the height of the Renaissance, oil painting techniques had almost completely replaced the use of egg tempera for panel paintings across most of Europe.
The fat over lean rule dictates that each additional layer of paint must contain more oil than the layer below it to prevent cracking and peeling. This technical constraint forced artists to develop a complex workflow where they would sketch the subject onto the canvas with charcoal or thinned paint before building up the image.
American portrait painter John Goffe Rand invented the squeezable metal tube in 1841. The portability of the tube enabled the practice of plein air painting, where artists could take their materials outdoors to capture the fleeting light of nature.
Linseed oil is the most general purpose drying oil used in oil painting. Safflower, walnut, and poppyseed oils are preferred for lighter colors because they yellow less on drying, though they dry more slowly and may not provide the strongest paint film.
The indirect painting technique creates luminosity by applying thin, transparent layers called glazes that allow light to penetrate completely through the paint and reflect off the white ground beneath. This method involves laying down an underpainting to tone the canvas before building up a mosaic of color swatches from darkest to lightest.