The Dictionary Of Photography

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

Home | About | Photography | Contact






Thinness of Negative
Thiosinnamine
Thinness of Negative. This may be the effect of three causes : first, under-exposure ; second, over-exposure ; and third, under-development. Thinness from under-exposure is usually caused by the whole plate veiling over before sufficient density can be obtained, due to the use of excessive alkali (see Under-exposure). In the case of over-exposure it is due to the energetic action of the developer, consequent upon the too great action of light (see Over-Exposure). In under-development the result is thinness, consequent upon the developer not reducing sufficient silver salt to the metallic state. This is generally distinguished from over- or under-exposure by the absence of fog or veiling.
Thiocarbamide (Ger., Siilphoharnstoff, Thiocarbamid; Fr. and Ital., Thiocarbamid). Synonym, Thiourea. CH4N^S. This organic compound was proposed by Dr. Bogisch as a fixing agent for chloride of silver, but its great utility is for the removal of stains of pyro or other developers, for removing green fog and silver stains, for which purpose the following solutions are recommended.
Thiocarbamide ............    20 grs.
Citric Acid............ ...     10 ..
Water           ...............      2 ozs.
or,
Thiocarbamide ... ... ... ...    20 grs.
Alum            ......... ......    20 ,,
Acetic Acid...............     10 minims.
Water           ... ... ...... ... 2 ozs.
Thiocarbamide in the developer has a remarkable tendency to bring about reversal.
Thiosinnamine (Ger., Allylsulphoharnstoff} Thio* sinamin; Fr. and Ital., Thiosinamiri). Synonym: Allylsulphurea. CSNH2NHC3H5 is an organic compound obtained by the action of ammonia on oil of mustard. It was suggested by Liesegang as a fixing agent for chloride of silver, but it has not come into general use. Like thiocarbamide it tends to bring about reversal if added to the developer. Thiosinnamine is said, like glucose, to prevent the evolution of gas in the case of the hydroxyla-mine developer.
612