_Photographic Collodion_ (Vol. vii., p. 314.).--In a former
communication I pointed out the wide differences in the various
manipulations prescribed for making the photographic _gun cotton_ by
several photographers: differences most perplexing to persons of small
leisure, and who are likely to lose half the opportunities of a
photographic season, whilst puzzling over these diversities of
proceeding. Suffer me now to entreat some one to whom all may look up
(perhaps your kind and experienced correspondent DR. DIAMOND will do
this service, so valuable to young photographers) to clear up the
differences I will now "make a note of," viz. as to the amount of dry
photographic gun cotton to be used in forming the prepared collodion.
On comparing various authors, and _reducing_ their directions to a
standard of _one ounce of ether_, I find the following differences:
viz., DR. DIAMOND (Vol. vi., p. 277.) prescribes _about_ three grains of
gun cotton; Mr. Hennah (_Directions, &c._, p. 5.) about seven grains;
the Count de Montizon (_Journ. of Phot. Soc._, p. 23.) eight grains;
whilst Mr. Bingham (_Supplement to Phot. Manip._, p. 2.) directs about
_thirty-four_ grains! in each case to a single ounce of ether.
These differences are too wide to come within even Mr. Archer's "long
range," that "the proportions ... must depend entirely upon the strength
and the thickness required ... the skill of the operator and the season
of the year." (Archer's _Manual_, p. 17.)