subject: Oil painting lessons - Working fat over lean [print this page] Oil painting lessons - Working fat over lean
You can use oil paints right out of the tube, but the consistency is stiff. Paint can have so much body that it feels like you're painting with ice-cold butter. Adding other materials to the paint either to dilute the paint or to thin the body of the paint by adding more oil increases the variety of ways that you can work with it.
So, aside from the actual paint that you work with, you also use a liquid to help mix the paint, thin it, and improve the overall flow of the paint from the brush onto the canvas.
Because of the way oil paint dries, you have to apply it in layers that don't interfere with the curing action of the paints. You can paint in a manner called alla prima, a fancy Italian term meaning a painting that's done all in one sitting. If you intend to work on the painting for a longer period of time, however, you must use the fat-over-lean method.
Working fat over lean means that you start the painting with a lean mixture of paint and solvent. You use only solvent as a wetting solution. Then, for the next layer of paint, you change to a mixture that uses a combination of solvent and linseed oil. For the last layers, you use the fattiest mixture, using more of the linseed oil to paint with.
What happens if you put a lean mixture of mostly solvent over a fatty layer of paint mixed with a lot of linseed oil? It doesn't work well. You may achieve a nice effect initially, but later, when you look at the painting, you see a whitish haze on the surface. This is called blooming, and it can't be removed.
Another problem that can happen if you ignore the fat-over-lean rule is cracking and crazing (also called alligatoring). A painting that cures unevenly will crack and age prematurely.
