A Manual Of Photography

SELECTION OF PAPER FOR PIIOTOGRAPHIC PURPOSES. 189 distinctness. From the various kinds of size which the manu- facturers use in their papers, it will he found that constantly- varying effects will arise. A well-sized paper is by no means objectionable ; on the contrary, organic combinations exalt the darkening property of the nitrate and muriate of silver. But unless we are careful always to use the same variety of paper for the same purpose, we shall be much perplexed by the con- stantly varying results which we shall obtain. No doubt, with the advancing importance of the art, the demand for paper for photographic purposes will increase ; manufacturers will then find it worth the necessary care to prepare paper agreeably to the directions of scientific men. Several of our paper makers are now paying much attention to the preparation of photo- graphic paper, and are considerably improving it. 1 have been most obligingly furnished by Mr. Sandford, of Paternoster Bow, with specimens of a great variety of Foreign and English papers, and from the care that gentleman is bestowing on this subject the most important advantages may be expected. All who desire to make any progress in photography must take the necessary precautions, or be content to meet witli repeated failures. The photographic peculiarities of paper mainly depend upon the sizes employed. The English paper manufacturers very commonly employ gelatine, and this in very different conditions. The French, on the contrary, use starch, and this, from the strong aiUnity existing between starch iodine, appears to be one reason, why the French paper is superior for the calotype in some of its forms. , , Besin soap is largely employed as a size. The soap is applied to the bibulous paper, and then decomposed by an acid water, leaving a fine film of resin spread upon the surface, susceptible of the highest polish. The following tables will exhibit the results of an extensive series of experiments, which were undertaken after the publi-. cation of Sir J. Herschel’s memoir “ On the Chemical Action of the Bays of the Solar Spectrum,” in which he has given a table of results, obtained witli different preparations on various kinds of paper ; but as he has not established the influence of the paper, except in a few instances, independent of the preparation, it be- came desirable to do so; and the result of several years' ex- perience has proved the correctness of the conclusions then arrived at. In pursuing this inquiry, it was found that the same descrip- tion of paper, from different manufacturers, gave rise to widely different effects; so that the most carefully conducted experi- ments, several times repeated, have only given approximations