Recently I was reading an article about "Tried and Tested Tools" which lists 28 tools that can help you in your artistic endeavors. (http://www.northlightshop.com/.) One item that I thought was really clever was the use of cellophane. Initially I thought "what....???" The artist in question uses it to check the tonality of their work. If doing a painting that is predominantly green he views his work through red cellophane and it shows him the tonal range. The idea is to view the work through a colour which is the complementary colour to the what is in the painting.
Then I thought to make it easier to use if you have a spare mat board from a frame you could glue it to the board and then you have a nice easy tool to use. I have tried this and it is amazing how it shows up the different values.
