_Difficulties in Photographic Practice._--Having met with some of the
difficulties that your correspondent G. H. mentions in his communication
(Vol. vii., p. 218.), I beg to offer a few hints which I think will be of
service to those who are trying the waxed-paper process.
With regard to the spots, it is not easy to know whether they are produced
by particles of iron in the paper, or by the oxide of silver. Le Gray says:
"If spots should form, produced by the oxide of silver, they may be removed
by pouring over the negative some acetic acid, and passing a brush lightly
over it."
The second difficulty, want of depth of tone or intensity in the negative,
may have been caused by too short an exposure in the camera, or not having
used the proper proportion of developing solution. Try the following:
4 oz. dist. water.
8 grains gallic acid.
When this solution has been filtered, add to it ½ drachm of the aceto-nitr.
of silver solution, and 1 drachm of acetic acid. I have generally put a
little camphor in the gallic acid solution, as recommended by Laborde. It
prevents the decomposition of the gallic acid, and renders the image
clearer and free from spots. A piece about the size of a pea for four or
five ounces of solution.
As to the third difficulty, I believe nothing but replacing the porcelain
dishes by glass ones will prevent the dirty marbled appearance in the
bottom of the dishes made of porcelain; they are generally rough and uneven
on the surface, and there are often what is called "kiln-cracks" in the
angular parts. Two months ago I bought two glass dishes; although they are
more than double the price of porcelain, I expect the annoyance of dirty
dishes is prevented. The glass ones are made quite round at the sides and
ends, and of course will be easily cleaned. I am informed they are made in
France, but they could be had of English manufacture.
The animal charcoal in the sensitive solution must be shaken up in the
aceto-nitrate solution; and when it has become quite clear, the solution
before using must be filtered into the dish.