LEVELLING SLAB (Fr., Dalle d niveler ; Ger., Nivellierplatte) A flat, smooth plate of glass, slate, marble, or other material, either attached to a frame work that may be levelled accurately by means is written in the reverse way with this solution, which must be used with care and not allowed to spread. Immediately the lettering appears white right through the gelatine, wash the negative quickly in water to stop the bleaching action and immerse in a "hypo" fixing bath, which dissolves out the bleached letters and leaves dear glass ; finally, wash and dry.
Numbering is not so difficult as lettering, and is, of course, done in the same way. The illus tration shows how the well-known pantograph can be applied to the work. In a frame the negative is laid film upwards. At the lower end is placed a strip of metal on which is engraved a set of numerals reversed. The lower end of the pantograph is made to follow the outline of the desired numeral, this being reproduced on a small scale at the upper end by a pencil, stylus, or needle-point.
The following method may be adopted where the titles are required in neat type characters : Set up the titles in type and get a good proof on enamel paper. Photograph this impression, using a wet plate for preference. Then from this negative make a transparency. When this
is dry, strip the film and attach it to the nega tive with an adhesive. This will give white lettering on dark ground. Black lettering on a light ground can be obtained by printing from a separate negative on to the paper or plate, using register marks to ensure exact position.
Titles on prints may be written in waterproof ink, black or white, each print being done separately, of course. The sensitive paper may be written on before printing, using Indian ink, red water-colour, etc., which, when toning and fixing, becomes washed away, leaving white lines. Finished prints may be written upon with the following chemical ink : Potassium iodide . 17o grs. 4o g.
Iodine . . . 17 „ 4 Gum arabic . • 17 „ 4 ,, Distilled water . 1 oz. 1,00o ccs.
This written upon the dark part of a silver print discharges the colour and appears white. Or, if preferred, a white pigment ink may be used. Black letters upon finished prints are made with black waterproof ink or by letterpress printing.
of screws at the corners, as illustrated, or intended for use on a levelling tripod (which see). as a support for plates to be coated with emulsion, or for other purposes where a perfectly even distribution is indis pensable.