Water Colours.—Water colours may be employed for all kinds of prints and slides. They differ essentially from dyes in that they do not sink into and stain the film, and therefore the surfaces need to be specially prepared so that they do not repel the colours ; also, a medium is necessary for the colours in order that they may not dry dull and dead. A suitable applica tion for prints is the following oxgall mixture ;— Purified oxgall . . r 5 grs. 6 g.
Methylated spirit . . I oz. 25o ccs.
Distilled water . . 4 „ 75o „ This should be well mixed and applied to the surface with a broad, soft brush, and the print when dry will be in a proper state to take both water colours and even oil colours. This pre paration is essential for albumen prints and others with a greasy surface, but may be omitted in the case of freshly-made P.O.P. or other gelatine prints.
A suitable medium to use in place of water for the water colours is made by dissolving a small quantity of the best gum arabic in sufficient water to cover it, and adding two or three drops of glycerine. This is not necessary for matt surface prints. An albumen solution must be used as a medium when colouring albumen prints, and some workers use it for all kinds of glossy prints ; it takes the place of the gum mixture, and is quite as good. The albumen mixture consists of the following : White of egg . . 1 oz. 3o ccs.
Glycerine . • 15 drops 15 drops Liquor ammonia' . 15„ 15 „ Ammonium carbonate 20 grs. 13 g.
Water . . . 2 drms. 7 ccs.
Whip the white of egg to a froth, allow to stand until clear, add the other chemicals previously dissolved in the water, and filter through muslin.
The choice of water colours is an important item ; there is a feeling in favour of colours in pans and not in tubes, but there is probably not much in the preference. Some are trans parent, others semi-transparent, and others, again, are opaque or body colours. An expe rienced worker may use any or all for print colouring, but for lantern slides transparent colours must be used. They are easily recognised by painting a few dabs upon glass and examining by transmitted light. Transparent colours are Prussian blue, crimson, alizarine yellow, Italian pink (which is really a yellow), olive green, sap green, purple madder and lake, and burnt car mine. The opaque colours are light red, yellow ochre, scarlet lake, ultramarine, Naples yellow, burnt umber, and Vandyke brown. The semi
transparent colours are sepia, madder brown, raw and burnt sienna, cobalt, and bistre. The above list is not by any means complete, but contains enough for average work. When white is required, Chinese white and no other should be used. For faces of portraits the colouring is usually put on very weak in the form of cross hatching, but for all other work colours are brushed on in the usual way, using plenty of the medium so as to weaken the colours.
Lantern slides can be coloured with trans parent water colours, but they need no special preparation, although many consider it advis able to harden them with formaline. Colours are applied in broad, even sweeps, and but little difficulty will be experienced except in skies, which more often than not are plain glass. When the Prussian blue—really the only pigment available for the purpose—is put on the plain film, brush marks are likely to show, but this defect is remedied by dabbing the blue while wet very gently with the finger-tip, or with a piece of kid glove stretched over the finger. The sky may be stained an even blue with dyes, and then given character with water colours. The slides also may be chemically toned to various tints and then completed with water colours. Considerable practice is necessary for lantern-slide work, and no small artistic skill, if it is wished to avoid the banal effects fre quently seen in commercial slides.
Oil in oils, particularly upon enlargements, is chiefly a professional practice, and the method of doing the work depends to some extent upon the materials used. Trans parent oil colours may be handled in a different manner from that adopted when body (opaque) pigments are used. The latter cover up the image, whereas the former, which give a rather weak effect, permit the shades and details of the picture to show through. For strength and high colouring the opaque colours are necessary, and for their use a knowledge of drawing and painting in general is requisite, as the photo graphic image is simply used as a base. The colours which will be found of the greatest ser vice are emerald green, Vandyke brown, indigo, Indian red, burnt umber, pink madder, light red, raw sienna, Naples yellow, yellow ochre, burnt sienna, crimson lake, raw umber, ultra marine, flake white, and ivory black.