Development.—Lay the print face downwards in a wide dish of cold water and leave it to soak for To min., when it may be lifted out while the water is changed, and examined to see if any portion of the pigment is dissolving out with the bichromate. After the second change of water, it may be dealt with face uppermost, unless these operations are taking place immediately under a brightly lighted window. Gently rocking the dish will probably remove most of the soluble colour, but if portions of the high lights prove obstinate in unveiling they may be delicately persuaded with a soft camel-hair mop brush. If the image is well exposed and fully set, the brush will come in useful in freeing other parts of the picture, as the worker gains more confidence and skill. Frequent changes of water, followed by an alum bath, will remove all traces of the bichromate stain. Warmer water is sometimes employed when the weather is cold, or when portions of the picture cannot be cleared by any other means. For delicate manipulations the print may be laid on a glass slab.
Multiple Gum.—For the higher Art purposes of the gum process more than one printing, either in the same, or in several different colours, is desirable. It is of the first importance that the paper selected for double printing be one which will not shrink or stretch seriously after prolonged treatment under water, arid, before attempting any ambitious essay, a sample of paper should be tested by pricking distances on it and examining after soaking and drying. A coat of size, made by dissolving t oz. of gelatine in 20 oz. of water, should be brushed over the selected sheet and then hardened with chrome alum, or, better still, formalin.
The simplest application of multiple gum is the printing in of clouds, which may be done by spreading a very thin, weak coating of pigment in the upper portion, printing under a cloud negative, and developing. When dry, the pigment can be laid on in its full strength, and the foreground and other features of the landscape printed and developed. Figures can be printed into a scene which lacks them ; over lapping is no serious matter to the gum artist, who, with his brush, can correct any anomaly on the wet print.
Where several colours are to follow one another by successive printings and developments a special printing frame will be required in order to secure exact register. Or, instead of the printing frame, the sensitised paper may be laid on an ordinary drawing board, then the negative, face downwards, secured in position by four pins, one on each edge of the glass, and the exposure decided by the actino meter. If the pins are in variably stuck through the same
holes in the paper there need be no fear of any serious irregularity. To enable the paper to withstand repeated sensitising and soaking there must be a good substratum of size.
The Colour Scheme.—For a few suggestions on this matter we are indebted to a very successful worker, Mr. M. Richard Witt, who recently read a paper on " Gum Bichromate in Colour" before the Photographic Society of Philadelphia. Mr. Witt suggests three colours : Indian Red or Venetian Red, Medium Cadmium Yellow, Indigo, or Prussian Blue.
In our colour scheme we must avoid too vivid a colouring, or the result, in combination with the photographic sharpness of detail in our negative, will be nothing but a chromo. The result desired should be more in the nature of a colour suggestion or an arbitrary colouring not necessarily approach ing the colours in the original landscape. It does not imply because the sky is blue or the grass is green that we should make our sky a brilliant blue or our grass a vivid green, for, as a matter of fact, the sky is more often any other tint than blue, and grass is not always green ; a cluster of trees in midsummer will show a variety of tones besides the deep green of the foliage, and so on. Should the beginner, however, wish to try for an actual reproduction of colours, we might take for example a conventional subject, such as a sunlit landscape in August, with fleecy clouds in the sky which occasionally obscure the sun, casting a soft glow over the country. In such a case it should first of all be remembered that we must not have a muddy, heavy sky, so that in our first coat, red, this pigment is entirely taken out of the sky, except for a faint deposit in the light shadows cast by the convolutions of the clouds ; a fairly good deposit is left in the trees, particularly in the trunks ; it is brushed out considerably from the grass, and if we have any water in the picture, a very thin coating is left there as a basis for the ripples.
The second coat, yellow, is also almost completely removed from the sky, except in the clouds, where a slight deposit should be left. In the trees we again leave a fairly good deposit, particularly in the trunks, and we leave a good, strong deposit in the grass for the representation of the diffused sunlight. The water should retain a very thin deposit of yellow.