[H] The scale actinometer is one requiring less attention.—Trans.
Masking should be resorted to to form a margin at least an inch wide round the four sides of the negative, either by painting round the same with Indian ink, or by attaching to the negative strips of opaque paper, or, better still, thin tinfoil.
Sunning.—When sufficiently exposed, i.e., when the brown picture with all its half-tones and details is complete, the plate is removed from the copying frame and placed, face downwards, upon a piece of black velvet, and exposed for a short time—five to ten minutes—to a good but not direct sunlight, so that it may pass through the glass plate and harden the back of the print layer. A sheet of ground glass may be placed over the plate to thoroughly diffuse the light, and prevent any scratches or damages to the back of the glass plate producing any detrimental effect upon the printing surface.
Washing the Plate is the next operation. The plate is removed into the dark room and placed in clean cold water, which should be often changed—every half-hour—unless an automatic washing apparatus[I] is used; this is continued until the plate no longer has a yellow appearance, and the picture is visible only as a slight brown image.
[I] Jefferies’s Patent “Perfect” Washer is a very suitable appliance, and may be used for Collotype plates, negatives, or paper prints.—Trans.
Hardening the Film is effected by soaking it for a quarter of an hour in a one per cent. solution of alum. The plate is again washed, and the surface evenly dried with fine tissue paper, and placed aside for at least two days that it may thoroughly dry.
An Alcohol Bath is used by many operators to immerse the plate in for half an hour after drying it with paper, perhaps with the intention of drying the film quicker, or to strengthen the layer and assist the formation of the grain, but there is no gain by this procedure, and, as the bath is an expense, it may be omitted.
The Damping Solution, or so-called etching fluid, is of much greater importance, and it is necessary that the plate be submitted to it before printing be attempted.
Tinted Grounds often enhance the appearance of prints, and may be imparted to them by the addition of an aqueous solution of red, yellow, or other suitable colour, to the damping solution, which is applied in the ordinary manner. The plate is superficially dried, inked up, and printed from in the usual way.