COLOURING PHOTOGRAPHS, ETC.
The three popular processes for colouring prints and slides are by means of aniline dyes, water colours, and oil colours. Colouring by the crystoleum process (which see) is also widely practised. Aniline dyes, although not so per manent as water colours, have largely super seded the latter, the dyes being so cheap and easy to use ; they are also transparent, and allow the details in the pictures to show through them, whereas some water and oil colours are body colours which hide all detail.
Photographs to be coloured with dyes or transparent pigments should not be deeply printed or given too warm a tone ; but these points are of no importance when body colours are used. A desk of some kind, or an easel, will be required for large prints, but small ones may be laid flat upon a table or held in the hand. Lantern slides and other transparencies are best held in the hand over white paper, or placed upon a retouching desk in such a way that the light comes through the slide, using preferably artificial light, as slides coloured in daylight are sometimes disappointing when viewed on the screen ; transmitted light allows the density of the colours to be better judged. Sable brushes of the sizes known as No. o (very small) to Nos. 5 or 6 will be found the most serviceable for average work, but others, as experience dictates, may be found useful.
Aniline Dyes.—These are the simplest of all colours in use, and may be used for slides and all kinds of prints, although they appear to best advantage on ordinary P.O.P. (gelatine) prints. Suitable dye solutions all ready for use may be purchased, the colours being put up in cheap sets and in very convenient form. Penny packets of dyes, obtainable at oil shops, are good enough for experimental work ; to prepare them for use dissolve first in I oz. of acetic acid or vinegar and make up to 2 oz. with water. The raw dyes may be dissolved and prepared in the same way, but very little of the actual dye need be used, as they are very strong, and a few grains will make a large quantity of coloured solution. The number of colours will depend upon the character of the work ; clever colourists, it should be said, can get all the colours they want by using only three—blue, yellow, and red—as by mixing these in suitable proportions any colour likely to be needed can be produced ; blue and yellow make green ; red and yellow, orange ' • blue and red, violet, etc. etc., the exact tints depending
upon the proportions of the two colours. The average worker will prefer ready-made dye solutions, and the following will be found the most serviceable : Blue, yellow, brown, olive green, scarlet, purple, orange, and pink. These dyes may be combined if desired, green and orange, for example, making citrine ; orange and purple, russet ; etc. The secret of success in using aniline dyes is to have them weak, building up the colours required by repeated washes of the dye rather than attempting to obtain in one application a colour of full strength. So important is this that the beginner is advised to begin colouring with dyes near to a water tap, so that as the colours are put on they may be largely washed off under the tap, the opera tions being repeated until the desired strength is obtained. The process is really that of staining or dyeing the print rather than painting, as the last-mentioned term is generally understood. If the print is mounted and cannot be satis factorily rinsed in water, the colours should be applied to the print very dilute, and immediately blotted with clean white blotting-paper. This prevents the dyes acting too quickly, and obliges the worker to proceed slowly and build up the colour. Blotting-paper is not suitable for use on slides, and the slides should be repeat edly rinsed instead, unless the dyes are applied sufficiently weak in the first instance. Prints do not usually require any preparation for colouring, but if much blotting or rinsing is to be done or the brush is at all stiff, it is advisable to harden gelatine films—P.O.P., bromide and gaslight papers and lantern slides—with a solu tion of i oz. of formalise in io oz. of water ; the fixed and washed slide or print is immersed in this for about ten minutes and then washed well. Alum should not be used for hardening previous to colouring with dyes, as it is apt to react chemically with some of the colours.