Early Work In Photography
A Text-book For Beginners

CHAPTER I. FIRST LESSONS IN PRINTING. The Action of Light. Materials Required for this Chaffer:-One |-plate printing frame (cost about 6d.), and one packet of 4 plate gelatino-chloride printing-out paper (cost is.), one pound of hypo (costs 2d.), one eep 5 X 7 porcelain tray (rod.), one piece clear glass 4$ x 3+ These may be obtained from any dealer in photographic goods. 30 EFORE we begin operations, it will be well for readers 6 to have some knowledge of the action of light in - photography, upon which all photographic processes are based. It is almost generally known that many substances undergo a decided chemical change under the influence of light, and this change is more or less visible in different cases. Note the effect of lunar caustic upon the skin; all our readers are acquainted with the decided black mark that clings so persistently after an application of this chemical, which is, after all, simply nitrate of silver (used by photographers), fused into sticks. Many otlier chemicals undergo a similar change under the influence of light, and are used, more or less, in various photographic processes. Of these we shall treat fully in a later book. Silver nitrate, then, is the most important chemical used by photograpliers. In conjunction with other chemicals, it forms the sensitizing agent in the photographic papers and dry plates of which we shall treat. Gelatino-cliloride “printing out” paper (often called "P.O.P.") is made by mixing certain proportions of nitrate of silver, chloride of sodium, citrate of potassium and gelatine; this mixture forms an emulsion* which is subsequently spread upon a sheet of paper and dried in the dark. The presence of chlorides increases the sensitiveness of sucli a paper (nitrate of silver, alone, would be practically useless for the purpose), but there always remains a slight excess of silver nitrate, which tends to give the vigorous image re- quired in this process. Before attempting a more interesting experiment, let us realize the effect of light upon this sensi- *See Glossary.