When the copy is to be enlarged instead of reduced, the gelatine cast is
put in a cold water bath, instead of alcohol. After it has swollen as
much as it will, the plaster mould is made as before. For enlarging,
the mould could also be made of some slightly soluble mass, and then by
filling it with water the cavity would grow larger, but it would not
give so sharp a copy.
* * * * *
STRIPPING THE FILM FROM GELATINE NEGATIVES.
We have frequent inquiries as to the best means of removing a
gelatino-bromide negative from its glass support so that it can be used
either as a direct or reversed negative, and it does not appear to be
very generally known that about two years ago Mr. Plener described a
method which answers well under all circumstances, whether a substratum
has been used or not.
If a negative is immersed in extremely dilute hydrofluoric acid
contained in an ebonite dish, say half a teaspoonful to half a pint of
water, the film very soon becomes loosened, and floats off the glass,
this circumstance being due to the solvent action which the acid
exercises upon the surface of the plate as soon as it has penetrated the
film.
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