Cleaning Leather Rollers without damaging them requires considerable practice. They are always scraped with a clean knife, and the operation should be performed in one direction, to ensure which it is advisable to mark one of the roller handles. Leather rollers not in constant use, before being put aside, should have their surfaces carefully and thoroughly rubbed over with tallow, which must, of course, be scraped off before the roller is again used.
Cleaning Composition and Indiarubber Rollers should not be effected by means of scraping, but their surfaces should be cleaned with turpentine, applied with a linen rag free from lint.
Cleaning the Plates.—Turpentine is used to free the surface from every particle of ink, and after the thorough evaporation of the spirit, the plates should be well washed in water to remove all trace of the damping solution, dried, and stored in a cool place. It is sometimes a matter of difficulty to remove ink from Collotype plates that have been printed from, but a simple method is to pour over the plate—as in developing a collodion picture—some lukewarm water. This will dissolve a thin layer of gelatine, and enable one to at once proceed with the work.
CHAPTER IX.
Finishing and Varnishing Collotype Prints.
RETOUCHING Prints.—Under the above heading Leon Vidal, in his work “Traité Pratique le Phototypie,” gives the following directions, which I reproduce from the “Photographic Archives.” Even with the utmost possible care in the preparation of the printing surfaces there will be required in most impressions a little retouching, if only to hide a few white spots. In large orders this cannot be carried to the extent it is in silver prints. It happens in printing that particles of dust find their way to the plate, and cause either light or dark spots in the impressions; the former are covered by touching with ink, the latter are removed with the erasing knife, and the white spot resulting from the operation is toned down with ink. This spotting is quickly performed. The paper being dull a colour should be used containing only a small proportion of gum; it will then be invisible. Prints which it is intended to varnish should not be spotted until they have been sized, unless printed upon a paper already impervious to the varnish. The colour most suitable of all is the actual printing ink thinned with turpentine, by using which the trouble is avoided of mixing any special colour to match the tone of the impression, as the two colours are necessarily identical. Another advantage gained by adopting this method is that the spotting may be completed before sizing, as the aqueous solution of gelatine will not cause it to run. For impressions in pure black the lithographic chalk is probably the best medium for correcting proofs, as the colouring matter will be found to well harmonise with the general appearance of the picture. A blacklead pencil, on the other hand, is quite unsuited for the purpose on account of the highly metallic appearance visible wherever the pencil has been applied to the print. Retouching or spotting should not extend beyond the removal of light and dark spots; the correction of larger faults should not be entertained, but a fresh printing surface produced. Faults present in the original negative should be carefully retouched and removed or reduced as far as possible. Should the white margins of the picture become soiled by contact with the inky mask or by finger marks, they may be cleaned with indiarubber ink eraser. The backs of impressions may also be cleaned in the same manner.
When copies have to be mounted on cardboard they may be either left with a matt surface or varnished. In the first case, the edges are trimmed, and they are then mounted upon the cardboard mounts. If the latter have been previously damped they will retain their flatness.
Rolling or Burnishing must not be done until the prints have completely dried, or the picture may be torn from the mount.