Half-closed Eyes.—The most common way is to half close the eyes, which shuts out details, but permits you to see the values. Some painters think this falsifies pitch, and prefer to keep the eyes wide open, but to focus them on some point beyond the values they are studying. This is not so easy to do as to half close the eyes, but becomes less difficult with practice.
The Blur Glass.—An ordinary magnifying-glass of about 15-inch focus, which you can get at an optician's for fifteen or twenty cents, will blur the details, and help you to see the values, because it makes everything vague except the masses. You can frame it for use by putting it between two pieces of cardboard with a hole in them, or you can do the same with two pieces of leather sewed around the edge. Of course the glass itself is all you need, but it will be easily broken if unprotected.
Do not try to look through the glass at your subject, but at the glass and the image on it.
The Claude Loraine Mirror.—This is a curved mirror with a black reflecting surface. The object is reflected on it, reduced both in size and pitch. It concentrates the masses and the color, and so helps to distinguish the relative values.
You can make a mirror of this sort for yourself by painting the back of a piece of plate glass black. The real Claude Loraine mirror is expensive.
The Common Mirror is also very helpful in distinguishing values. It reduces the size of things, and reverses the drawing so that you see your subject under different conditions, and a fresh eye is the result. Place the group and your painting side by side, if you are painting still life, and look at both at the same time in the mirror. Do the same with a portrait and the sitter.
Diminishing Glass.—Much the same effect can be had by using a double concave lens. The picture is not reversed, but it is reduced, and the details eliminated.
In using any of these means you must remember that it is always the relations and not the things you are studying; and the most useful of these aids is the blur glass, because you cannot possibly see anything in it but the values and color masses, everything else being blurred.