BLACKENING APPARATUS Only a dead black is suitable for the interior of a camera, as a glossy black would give rise to reflections.
Blackings should be tested upon pieces of metal, wood, leather, etc., before applying to the apparatus. Recipes are as follow : Brasswork.—To blacken camera brasswork, clean with fine emery, rinse, and immerse in a saturated solution of copper nitrate for about two minutes. Then take out, heat over a Bunsen burner or ordinary spirit flame, and repeat the process several times. To make the copper nitrate, dissolver oz. of copper filings in 2 oz. of nitric acid ; do this in the open air, and stir with a glass rod to assist dissolving.
Zincwork.—Clean and rinse as before, and immerse in a solution of copper chloride 45 grs., zinc nitrate 3o grs., and water 4 oz., to which is added f oz. of hydrochloric acid. Finally, rinse and dry.
Tin.—Use carbon black mixed with the least possible amount of French polish. Excess of
polish makes it glossy. A dye can be used instead of a pigment ; for example, boil together r oz. of water, 15 grs. of borax, 3o grs. of shellac, and 15 minims of glycerine. Maintain the boiling till dissolved, and then add 6o grs. of nigrosin.
Bellows Interiors.—Use a solution of shellac in methylated spirit coloured with lampblack.
Camera Interior (Woodwork).—Dissolve f oz. of shellac and f oz. of borax in xo oz. of hot water, and add about f drm. of glycerine and sufficient aniline black (soluble in water) to form a good solid black. Two coats should produce a rich velvety dead black. Another recipe is : Aniline black 5o grs., gum shellac ioo grs., methylated spirit 2f oz. Negative varnish mixed with powdered lampblack may also be used.
Lampblack mixed with gold size and turpentine makes a good dead black for general use.