THE PHOTOGRAPHIC JOURNAL. January 1, 1859, p.3
ONE of the greatest difficulties the photographer has to contend with at the present day, is in the papers manufactured expressly for photographic purposes. Of Foreign papers, we have Papier Saxe, Canson's, and Marion's; of English, there are Hollingsworth's, Harrison's, and others Although the pulp of the papers of these different makers is in all respect the same, being composed of linen and cotton rags, yet very different photographic properties are produced from them in consequence of the sizing being different English papers are, for the most part, sized with gelatine, while those of the Continent arc sized with fecala, or starch and resin. soap. Now, the sizing greatly influences the colour of the proof; papers sized with gelatine give very red hues in the printing-frame, while those sized with starch are sepia or violet: still the quality of the sizing does not influence the colour of the proofs so much as the quantity; for by increasing the quantity of starch in the paper, hues as red. as those from gelatine may be obtained.
The sizing not only makes the proofs more vigorous, but also makes them sharper and more delicate. A proof taken on unsized paper, is dull and leaden in hue, and in every respect repulsive. If but slightly sized with albumen, the unsized paper is but little improved: strong starch produces bright orange hues, and if the unsized paper be immersed in a strong solution of gelatine (5 per cent.) fine reddish hues are produced.
The quantity of sizing contained in the paper as delivered by the manufacturer is insufficient for photographic purposes; for proofs taken on plain paper, although very pleasing and satisfactory in an artistic; point of view, lack transparency in the shadows, and that general brilliancy of tone which is indispensable to suit the popular taste. However, at the present time, the extra sizing is carried to excess, and except in stereoscopic pictures should be avoided. For portraits, landscapes, architectural subjects, &c., paper prepared with a mixture of albumen and water, in equal parts, has quite sufficient surface and gloss to bring out all the detail, and at the same time to secure adequate transparency in the shadows.
In fact, the higher albumenized paper now sold is to be regarded with suspicion, as the very high glaze is not due to pure albumen, but to an admixture or adulteration, either dextrine or gelatine; the presence of the latter is recognised by the chocolate red colour of the proofs when removed from the pressure frame; and if the wet proofs are allowed to dry while in contact, they adhere together and are spoiled.
Oxide of silver, in combination with gelatine, and exposed to light, becomes an insoluble black varnish, which reflects a golden red line; but when the combination is first made, the compound is of a mahogany red colour. These facts explain the causes of the variety of hues given by papers sized with different materials. If the paper be unsized then the salt of silver enters into combination with the fibre of the paper, and the silver tends to decompose and reduce itself; or perhaps, as suggested by Schönbein, ozonized oxygen plays a ,part in this change. But in the case of sized paper, the particular affinity of the sizing material for the silver overcomes the disposition of the salt of silver to combine with the paper, or to reduce itself, and forming the compound spoken of, the chemical action is not exercised on or by the paper itself; the picture therefore requires both greater sharpness and the red hue due to the sizing material. Whatever the kind of sizing employed, or the quantity, it does not appear to have any influence upon the rapidity of printing; other things remaining the same.
Nor does the thickness of the paper appear to have any influence upon the result, beyond what is due to the greater abundance of sizing it contains; but thick paper is easier to manipulate, although more liable to tear while wet. From what has been stated, it appears that it is a matter of indifference what paper is used, provided- it be not used plain, but sized with albumen, dextrine, gelatine, or starch. Some attention must be paid however to the sizing strength of equal weights of these materials, as the results will be materially influenced thereby. Of all the sizing materials, albumen, more or less diluted with water, is to be preferred.