The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Lead, Chromate of                                                Leimtype
and crystallisation. It is met with in white crystals |usually massed together, and has an intensely sweet taste, and a faint smell of acetic acid. It is used as an addition to some combined toning and fixing baths, and has been suggested as a hypo-eliminator but the benefit is doubtful. Solubility; 60 per cent, in cold and 200 per cent, in hot water; 12 per cent, in alcohol; insoluble in ether.
Lead, Chromate of (Ger. Bleichromat; Fr., Chromate de filomb; Ital., Cromato di fiiombd). PbCr04 = 323-5. Prepared by double decomposition of lead, acetate, and chromate or bichromate of potassium. It is a yellow insoluble powder, and is only used as colouring matter for certain dark-room fabrics.
Lead, Nitrate of (Ger., Bleinitrat; Fr., Azotate de filomb; Ital., Azotato di fiiombd). Pb(N03)2 = 331. Synonym : Plumbic Nitrate. Made by dissolving litharge or white lead in nitric acid, evaporating and crystallising. It occurs in hard, white, opaque, octahedral crystals. It is used in Intensification {q.v.) and as a constituent of some combined toning and fixing baths.
Lead, Toning with. A solution of acetate of lead has been proposed as a toning bath for albumenised and gelatino-chloride papers. The following formula has been suggested: -
Lead acetate or nitrate ... ...... oz.
Sodium hyposulphite         ... ... ... 4 ozs.
Distilled water ... ... ... ... 20 ,,
The toning action in any bath of this character is due to the formation of sulphide of lead.
Least Circle of Aberration is the smallest possible section of the cone of rays of light emergent from a lens.
Leimtype. A special process for the production of half-tone blocks invented by Husnik of Prague. A film of bichromated gelatine is exposed, then mounted by the exposed side on a rigid block, and developed by a solvent. The printing block is therefore somewhat similar in nature to a carbon print, having a specially high relief. The screen may be used to give a print-ing grain. (See Carbon Printing, Fish Glue Process, and
WOODBURYT YPE.)
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