Yesterday I talked about making your own tonal value finder or tool to help you when painting. Today I thought I would walk you thru it.
First you need the following:
red transparency film or acetate (check in scrapbooking supplies or even a clear red plastic doutang will work)
Cut your red film to the size desired. Cut out 2 pieces of cardboard about 1 inch larger than red film on all sides.
Using your exacto knife cut out windows in your cardboard about 1/2 inch smaller than your red film piece.
Tape your red film in between your two cardboard pieces. Then tape the two cardboard pieces together around the edges.
Because I will be using mine in my field kit I taped all around the edges with duct tape so it will hold up to daily use.
To show you how this works here is the wc sketch of St. Paul's both before and after changes. The red mutes the colors to get you to focus on the value instead. This is a good tool to have when you don't have access to a computer, photocopier,etc. to view your painting in black and white.
Hope this helps.