To make a dull black stain for the interior of a camera, mix powdered lampblack and French polish, using of the latter only just enough to make the black adhere. Too much will produce a polished appearance. Another recipe is : Aniline black, l00 gr.; gum shellac, 200 gr.; methylated spirit, 5oz. Dissolve thoroughly, and apply with a soft brush quickly. Negative varnish and powdered lampblack may also be used.