INSENSITIVE TISSUES.
All insensitive tissues are made with a single sample of hard gelatine. They are stocked by dealers and must of necessity be fit for use at any season of the year, to say nothing of those exported to hot climates.
TRANSFER PAPERS.
Papers of many kinds are necessary for single transfer prints, the tint of the paper must blend and harmonize with the tone of the tissue or by contrasting help to produce a pleasing effect. For prints of warm tones such as red chalk, terra cotta and the various tints of sepia, a yellowish or cream-toned paper forms the most harmonious basis; the various tints of black, blue, and purple look best on a slightly bluish-tinted paper. For instance, a copy of an old engraving in tissue, of the brown tone of the original would be utterly spoilt by a blue-tinted basis. The above remarks apply only in a limited degree to double transfer papers which in general use are confined almost exclusively to portraiture. Such papers are sometimes modified by tinting mauve, rose, opal, etc., etc. Such tints are only in small demand and are in all cases confined to papers coated with enamel preparations. The best and most durable form of double transfer paper is that prepared on fine chemically pure paper with colourless gelatine and made insoluble by the smallest possible quantity of chrome alum, entirely without white or tinted pigment of any kind. The best variety of double transfer paper only differs from the finest form of single transfer paper in having on its surface a rather thicker and softer coating of colourless gelatine.
All transfer papers, either for single or double transfer, may be coated in the same way as tissue, with the exception of those having a very rough surface. All drawing papers and in fact all papers of very rough surface are prepared by brushing over their surfaces several coatings of a very thin solution of gelatine containing a larger proportion of chrome alum or formalin than is used in making ordinary single transfers. A flat camel-hair brush is best for this form of coating, care must be taken to avoid air bubbles.
FLEXIBLE TEMPORARY SUPPORT.
Is paper coated with a gelatine solution in the first instance, and after drying, again coated with an aqueous solution of shellac.
SENSITIZING THE TISSUE.
Pour the bichromate solution into a deep flat dish (porcelain, ebonite, zinc, wood or tin) to the depth of half an inch to an inch; place a sheet of tissue in it face upwards, remove air-bubbles with a camel-hair brush or soft sponge, using as little pressure as may be; turn the sheet and remove bubbles formed on the paper, turn the sheet again face upwards, and passing brush or sponge gently over the surface, keep it evenly wet until it is fairly limp; remove from the solution, place face downwards on a perfectly clean glass or zinc plate, squeegee to remove excess of solution, blot or wipe with a soft cloth, remove any solution from the fingers, lift from the plate, handle by edges only, clip to a line, small sizes by one corner only, larger sheets by two corners, leaving a little slackness between the two clips to allow for contraction in drying, otherwise the sheet will be distorted and difficult to press into contact with the negative.
The sensitizing may be done in ordinary daylight. The drying must take place in a room from which actinic light is excluded, and in a current of warm dry air, free from impurities, such as the products of combustion from burning gas, or an escape of sewer gas, etc., and at a temperature not higher than 120° F. The drying should be done as quickly as possible, otherwise the tissue's keeping property will be greatly reduced, and in all probability a thin film formed on the surface, of insoluble gelatine, known to printers as "decomposed tint," degrading the high-lights, and, except in the case of very "hard" negatives, spoiling the work.