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Sizing

water and oz

SIZING Raw papers generally need to be sized before sensitising, because the size fills up the pores and keeps the image on the surface ; in some cases, also, it increases the sensitiveness. As a general rule, sizing improves any raw paper. The sizes most used are arrowroot and gelatine, and the paper can be floated on one of these or brushed over with the substance. In the case of gelatine the paper may be wholly immersed.

Arrowroot.—Of the many formulze known, that due to Duchochois is as follows : Arrowroot . grs. 25 g.

Glucose. . . . 20 ,, 5 ,, Water . . . . io oz. I,ouo ccs.

Mix the arrowroot and glucose with a little cold water, add the remainder hot, and boil up the whole in a porcelain dish. Cool, skim and strain through muslin before use. The above is suit able for the iron printing processes, namely, blue print, kallitype, etc. Other formula; are given under separate headings.

Gelatine.—The following is suitable for print ing with iron salts : Hard gelatine 5o grs. 25 g.

Water . . . . io oz. i,000 ccs.

Alum . . . . 15 grs. 7.5 g.

Alcohol (pure) . 2 Oz. 220 COS. Soak the gelatine in about 9 oz. of the water for about an hour, heat until dissolved, dissolve the alum in the remaining water, add to the gelatine, and lastly the alcohol. After coating, dry for three minutes and coat again. For plain silver paper, dissolve 5 grs. of gelatine in io oz. of water, by aid of heat, and then dissolve therein 6o grs. of ammonium chloride. Immerse twice as above.

Gum Arabic.—For iron papers, prepare a weak solution of gum arabic (5 or 6 grs. to the oz. of water), and brush over the paper.

Resin, Iceland moss, and agar-agar are also used.