delicate tints, while the other giving full tones. By repeating this series of operations a sufficient number of times, it becomes possible not only to push the range of gradations to the utmost at both ends of the scale, but to emphasise any part of the scale ; moreover, masking of the negatives at any stage gives a full power of emphasising any part of the subject. Thus it is that gum-bichromate is more under the personal control of the worker than any other printing method.
Paper for Multiple Printing. Too much care cannot be taken in selecting the paper, as any considerable stretching or deforma-tion in working is fatal; register or exact correspondence with the negative being destroyed by stretching or deformation. The recommendation given above, to use a paper tending to rough-ness in order to assist development, does not apply when the multiple system of printing is adopted; hence paper with any kind of surface may be selected. The paper should be " hand-made," or, at any rate, it should have been made or moulded in single sheets, as in the old system of hand-making; and not as a band, like ordinary machine-made papers. The difference in quality is this: Paper made in sheets by the hand-moulding process has no prevailing direction for the fibres, neither has it any prevailing direction of strain or compression; true the " hand-moulding " process may be assisted by machinery; indeed it may practically become a mechanical operation, buc the product is very different from the paper made as a long band, and in addition strained or put into tension by a system of rollers.
Test for "Hand-made" Paper. The following will be a sufficient test for "hand-made" paper as defined above, provided that the material is not too much artificially indurated by any material impervious to water. A square piece with 18- to 20-in. sides is very accurately cut from a sheet laid on a smooth, flat board, and well sponged over many times with water. If, after several turnings and several spongings, the expansion of the sheet is found to be equal in both directions, the paper may be considered "hand-made," or, at any rate, moulded as sheets rather than in a band. Hand-made papers of first rate quality can be had; for example, the Van Gelder papers, Whatman's drawing papers, also the heavy Japanese papers. The paper selected should be rather thick: a paper at least twice the weight of that upon which this Dictionary is printed being desirable in