DEVELOPING.
In development, the paper, on coming from the frame, is lowered, face down, quickly and evenly, into a hot saturated solution of potassium oxalate, and de velopment is instantaneous. There is little or no control possible beyond al terations made to the developer before hand. The developed prints are placed one by one in a 1 in 60 solution of hydro chloric acid ; this dissolves out the faint iron image, without apparent loss of inten sity, and the iron must be thoroughly re moved, as any residue would cause the whites to turn yellow. It is imperative therefore, that pure and not " commer cial " hydrochloric acid be used, as the latter already contains iron. The prints should be passed through three successive baths, remaining three minutes in each, before the final washing for fifteen minutes. Soft water is preferable for washing, and may with advantage be made slightly alka line with a little washing soda. The paper
now in general use develops in a cold solu tion, although many workers prefer it slightly warmed. The print may be pinned to a board or laid on a glass and developed with a brush. Glycerine applied to certain portions prevents the developer sinking into them rapidly, and allows the other parts to approach them in printed effect. Sepia platinum paper may also be pur chased, or sepia tones may be produced on the paper described herein by the ad dition of sufficient of a saturated solution of mercuric chloride to the developer. Further details of commercial papers are unnecessary, as directions for their use are supplied by the manufacturers. The de veloper recommended is different, in some cases, from that given above.