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Standard

relief, process, glass, solution, plate, gelatine and piece

STANDARD SPIRIT.—A mixture of alcohol and water having a sp. gr. of '92 at 62 deg. Fahr. It contains nearly equal parts of absolute alcohol and water.

STAND, CAMERA.—See Camera Stand and Tripod.

STANNOTYPE.—This process may be termed a simplified Woodbury process. On refer ence to the description of the latter, it will be found that one of the principal requirements is a costly hydraulic press, with which to form the printing mould by pressing the gelatine relief into the lead surface. The object of the stannotype process was to do away with this costly machinery, and bring the process within the reach of all. A careful consideration of the principles involved in the Woodburytype process will show that if a gelatine relief were produced from a positive instead of a negative, this relief would serve as the printing mould in the same manner as the impressed lead, were it not for one serious drawback, and that is, that being of gelatine it would be destroyed when it received the necessary wetting. This drawback was overcome by Wood bury after a long course of laborious experiments by a most simple expedient.' It was simply by protecting the relief by means of a sheet of tinfoil, pressed well into contact with it.

The first thing necessary in the preparation of the relief is a positive transparency. This can be produced by any of the well-known methods, that process being most suitable which gives the greatest range of density. This transparency, it should be noted, must be reversed as regards right and left, unless the picture is one that can be printed reversed without being noticeable. The single-transfer carbon process is the one generally used, the image being intensified with potassium permanganate. Finally, the transparency should have an edging of clear glass about *n. width, and the highest light should be quite clear.

The transparency having been made, the relief is next made from it, as in the Woodbury type process. This may also be done by laying a piece of moist paper upon a sheet of glass, and coating it with a gelatine solution ; when set, both are detached from the glass and hung up to dry. It is afterwards sensitized in a bichromate solution and printed from with the positive. If paper be used as the support, the side farthest from the paper is, of course, brought into contact with the positive, and that side is afterwards attached to glass, either by means of an indiarubber solution, or by coating the glass with gelatine containing a little bichromate solution, and drying the film in the sunlight.

By whatever means the relief is produced, it should, after being developed, be allowed to remain upon the glass plate, which should be plate glass and rather thick.

The next operation is the protection of the relief with the tin-foil. If only a few hundred copies are required to be printed, ordinary tinfoil will do, but if a large quantity are necessary, special steel-face foil must be employed. The tinfoil must be of perfect quality and free from pinholes. These may be detected by holding the sheet up to a strong light, and any piece con taining them should be instantly rejected, as the smallest hole will allow the gelatinous ink to wet the relief beneath, and produce a white spot, if nothing more serious.

A piece of the perfect foil, a little larger than the relief, is laid on to a clean sheet of glass, and carefully flattened and rubbed out smooth with a velvet pad. Those used for brushing silk hats are very serviceable for this purpose. The relief is then prepared to receive it. The edging, which is in high relief, is first coated with a thick solution of rubber in benzine, and when this is set the whole surface is flowed with a thin solution of rubber. Burton recommends gum para, a good strength of solution being two grains to the ounce. Pure benzine will serve as a solvent, although chloroform is much preferred. When this indiarubber film has set, the tinfoil is laid carefully over it and pressed well into contact with the velvet pad, and then the plate holding the relief and foil is passed through two rubber or rubber-coated rollers. The domestic wringing machine, fitted with indiarubber rollers, serves excellently for this purpose. The rollers are separated, and the plate inserted, so that the rollers cross the center of it. Pressure is then ap plied, and the plate moved backwards and forwards so that the tin face is pressed well into all the parts of the relief. The back of the glass is then cleaned, and the face surface of the now perfect printing mould carefully oiled with a little piece of flannel with a drop or two of mixture of olive and paraffin oils. The mould is then ready for printing from in the same manner as with . the Woodburytype process (q. v.)