Crescofylma Crystal Varnish
the paper is not quite dry, the moisture will sometimes diffuse into the backing pad, and the paper will contract; this con-traction being sometimes as much asof an inch to a sheet, even though the paper seemed quite dry to the touch.
Crescofylma. A name applied to a commercial preparation which probably contains either free hydrofluoric acid or an acidi-fied fluoride, and used as a means of floating the negative film off the glass, in order that after becoming stretched it may be mounted on another plate, or otherwise used in its expanded form. (See Negatives, Stripping of.)
Critical Angle. When light passes from a dense medium to a rare medium under an increasing angle with the perpen-dicular, an angle will be reached at which the refracted ray should make an angle of 900 with the normal. This is called the critical angle, and then internal or total reflection sets in.
Crossed Lens. The form of single lens which has the least spherical aberration; double convex, and best with radius of posterior surface about six times that of anterior surface.
Crystal Cube, or Crystal Miniature. Mr. Henry Swan's device for showing stereoscopic effect. A cube of glass is made up of two prisms, the angle of division being so adjusted in relation to the refractive power of the glass, that one eye sees an element of the stereogram by transmission, and the other eye sees the second element of the stereogram by reflection. The effect is as if a solid object were embedded in the glass.
Crystal Varnish. This is specially designed for varnishing lantern-slides and transparencies, and is made by dissolving -
Gum dammar ... ... ... ... 25 grs.
Benzole ... ... ... ... ... 1 oz.
another formula being
Canada balsam ... ... ... ... 5 parts.
Shellac (yellow) ...... ... ... 160 M
Sandarac ... ... ... ... ... 170 ,,
Alcohol ......... ... ... 1000 ,,