|Lucky students with their red value eyeglasses|
Just as a reminder, the purpose behind it is to help a painter determine relative values. If you look through it at a scene, everything - trees, lawns, buildings - will all be seen as different shades of red. If one shape is a lighter shade of red than another shape, you paint it accordingly. (Not in red, of course, but in the observed actual color.)
But although it's a great teaching tool, you can't rely on it as an accurate interpreter of values.
It alters vales for certain colors. Reds turn a little lighter. Lights, especially white, turn darker. Green trees and gree fields are observed as being much darker. If you were to paint them this way, your landscape would look stunningly wrong. Here's what a scene looks like through mine. The white reads as darker and the reds a little lighter, and so the letters disappear:
Although there are ways around this - taking an image with your digital camera and viewing it in greyscale might be one way - the best approach is simply to learn how to distinguish values in the landscape. It's not hard, but it does take practice.
By the way, I mentioned in my last post that the Spring Sale is on! Visit my Studio Store.