The Dictionary Of Photography

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

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in the high lights, leaving the negative much thinner in the high lights than it originally was. A little practice with waste negatives will give the required power of judgment. A negative which is hard from under-exposure, and one which has been fully exposed but is hard from over-development, will not present the same appearance during redevelopment, after rehalogenis-ation. If the former be redeveloped right through, the high lights will appear black at the back of the plate; the high light in the fully exposed negative will never appear black, however far the redevelopment may be pushed, and as the layer of white-coloured silver present in this case will not be dissolved out by the hypo, an allowance for this must be made in re-development, or the negative will still be too dense. There is no theoretical objection to the negative being again treated by the process to obtain the required reduction, but in practice there is an additional risk of stains appearing the second time. It is better to err on the side of under-development and intensify if necessary. In this process, as in all others, great cleanliness is required, and the plate must have been thoroughly freed from hypo before proceeding to rehalogenise. If hypo or other chemicals be present, thin patches and dark spots will show. If there are grease-spots or finger-marks on the plate, irregular action will take place. It is best to take but one trial print from the negative, and exercise great care in doing so if rehalogenisation be thought needful. When operating on old negatives I wash them gently with dilute ammonia to get rid of, if possible, grease-spots before beginning the process."
Head-Rest. An apparatus used for maintaining an exact position and steadiness of a sitter during exposure. Great prejudice exists in the minds of most people against it, due to its use having been abused to such an extent as to become an absolute instrument of torture. In all cases the head-rest should be adapted to the position of the sitter's head and applied gently, and the head should never be strained to the position of the head-rest.
Hectogram One
hundred grammes. (See Weights and Measures.)