I keep written information on a painting from the very beginning, i.e., size of canvas, linen or canvas, a brief description of the subject matter, for identification if the title is not yet known , the color used to tone canvas, notes on the colors used in the painting and general information about the painting. For example, problems to work out, if any, general observations and thoughts regarding the subject matter, composition, as well as details on color mixtures. Good and bad information are addressed at the beginning of each painting session, I always read my notes from the previous session and if I have problems to resolve I begin by addressing them first. As I work through the issues I record the information in my journal on how I resolved them, and why.
Finally, I use my phone camera because it's always handy to photograph the days work. It is a terrific reference tool. You can see your painting in its metamorphosis to completion, and the photos are good at spotting mistakes as well. When you've been away from the painting awhile, take a look at the photo you took of the days work. You may be surprised what the photo will tell you, good or bad.
* A note on the painting at the top left of this page, The Cabbage Pot, is NOT finished. It is still in the very early stages. There are areas of the underpainting still exposed. I wanted to show the first day, the beginning of the painting, which is toning the canvas and painting the subject matter by removing the paint with a brush while the paint is still wet. This process has to be completed while the thinned oil paint remains wet. Sometimes it is necessary to add paint as well to achieve the desired results, I didn't do this in the Cabbage Pot. This is a one time process that can only be achieved while the thinned paint is wet.
The photo at the top of the page is on it's way but still in progress.