Leather rollers when new should first of all be warmed in front of a brisk fire, and when warm rubbed with a piece of Russian tallow until the leather will not absorb any more. Then allow the roller to stand twelve hours {155} and repeat the operation; then take some middle varnish, smear some of it along the roller, and on a clean slab roll vigorously, and repeat the operation two or three times, scrape the roller with the grain, then roll up in varnish, allow to stand all night, scrape again, roll up again next day, scrape, then roll up with collotype ink, scrape and roll up, repeating this until the roller takes the ink evenly. After each time of using, scrape the roller before putting away, and if, after using, the roller is likely to be some time before being wanted again, after scraping smear it with Russian tallow, and wrap it up in paper, scraping it before rolling it up in the ink again.
Glue rollers should be hung up after use in a cold place, and before being put away should be coated with fatty ink, and just before using should be rolled clean upon a piece of rather fluffy paper; washing glue rollers in turpentine is not to be recommended, as it tends to harden them, and deprives them of their feeding quality. Glue rollers can be bought ready cast, and it is advisable to so buy them; any dealer in typographic material will supply them of a suitable quality, if the purpose for which they are required be stated at the time of ordering. The “durable” composition being very good for collographic printing, it may be purchased and used for the rollers, for printing from a heliotype skin, instead of the mixture given previously. For roller No. 2, add two ounces of gelatine previously soaked in cold water, and as much water squeezed out as is possible, then add this to the “durable” composition, and stir until the gelatine is melted and well incorporated with the composition.
These rollers may be cast upon the bare stock, without the India-rubber sponge, if preferred, but the India-rubber sponge makes the roller much lighter for use, which is a great consideration when long numbers are printed straight away.
These remarks are applicable to the rollers used in the work described in the previous chapters. Too much care cannot be given to the rollers. The skilled printer who has feeling for his work will soon learn to regard his rollers as the magic wands which produce his results. And well he may.
The ink used for heliotype printing is the best chalk ink as purchased in tins, brought to working consistency by mixing with lard, the two ingredients being well mulled on the slab. Varnish must not be used, lard being the best. Cocoanut and olive oil are also good. {156}
HELIOTYPE SKIN
is composed of a mixture of gelatine, glycerine, chrome alum, bichromate of potash, and water, dried upon a slab of thick plate glass. The surface of the plate glass must be very finely ground with emery powder (great care being taken that there are no scratches or holes, or they will spoil the skin), then thoroughly cleaned, and waxed with a solution of beeswax in benzole, a good plan being to first of all smear the glass with the wax, and then polish as much off as possible with an old linen duster (clean), then sprinkle with clean benzole, and with a fresh duster polish the plate thoroughly, noting well that wax marks will spoil the skin.
This waxing need not be done every time a skin is made, but at intervals of every three or four skins.
The waxed glass requires levelling, so that the gelatinous mixture will set of an even thickness; therefore, a levelling stand must be provided, as well as a good and true spirit level.
The gelatinous mixture is dried in an oven (see Drying Oven in chapter on Collotype), at a temperature not exceeding 80° F., the time occupied being from thirty to forty hours.