The main reason to keep a diary (I have several full ones now) is basically to remember any ideas I have for future use, to make notes on developing these ideas so that I can come back to the ideas later, to think about the process of what I am doing - I tend to make a lot of notes about the colour of things and what layers of colour I can sense in the image and to experiment with composition of images before I paint them. I also make notes on the line, form and shape of images. I also write my opinions on other artists works that have captured my attention and try to note why I like their work and why their work moves me to include it in my diary.
So my diary is basically made up of:
-cuttings from magazines / old calendars - mostly flowers / fruit and geisha
- cuttings or greeting cards by other artists I admire or who are doing things I aspire to
- Newspaper articles on other artists I admire
- ideas jotted down
- test colours
- photos of flowers from different angles
comments, opinions and ideas for the future
Some artists - more illustrator types - spend a lot of time on their diaries, which are fascinating pieces of decorative artworks in themselves, however, mine is more of a practical usage diary that I use as a reference. You can see some examples above and below where I use it to experiment with composition, colour and collect reference pictures for my paintings...