I have experimented with carbonate of lithia as an accelerator, and I
have obtained with it rather favorable results. However, in opposition
to Mr. Wickers, I have always found that carbonate of lithia, used
even in larger doses than those recommended by this author, was not
sufficiently active, and that development had to be too much prolonged
in order to obtain prints of good intensity. I have also observed that
the prints developed by this process were as often fogged as when I
made use of carbonate of potash. The oxides of alkaline metals or
their alkaline salts are not the only accelerators susceptible of
being used in pyro development. Two oxides of the earthy alkaline
metals, lime and hydrate of barytes, may also be used as accelerators.
I will not insist upon the second, which, although giving some
results, should be rejected from photographic practice on account of
its caustic properties, and of its too great affinity for the carbonic
acids in the air, which prevents the keeping of its solutions. This
objection does not obtain for the first, provided, however, that
ordinary lime water is not used, but a solution of succharate or
sucrate of lime. In my experiments I have made use of the following
solutions:
_Solution A._
Pyrogallic acid. 10 grms.
Sulphite of soda. 20 "
Citric acid. 2 "
Water. 120 "
_Solution B._
Water. 1000 "
Sugar. sufficient quantity to triturate.
To which add a sufficient quantity of pure lime to saturate the sugar
solution.
In this manner we get a highly concentrated liquid, very alkaline, and
which keeps for a considerable time. To develop, I mix:
Water. 80 cubic cent.
Solution A. 2 " "
I throw this over the plate, and allow it to remain for a few moments,
agitating, then I add to this bath gradually and according to the
results obtained, from one to two cubic centimeters of the solution B.
These solutions should be made with a great deal of care and prudence,
as the sucrate of lime is an accelerator of very great energy.
Moreover, according as the plate has been more or less exposed, we may
add to the developing bath a few drops of a solution of citric acid,
or of a solution of an alkaline bromide. We obtain in this way very
soft prints, sometimes too soft, which, however, are not more free
from fogging than plates developed with hydrochinon (new bath), or
pyro having for accelerators ammonia, potash, soda, carbonate of
potash, of soda, or of lithia. I do not give this process with sucrate
of lime as perfect, but I give it as perfectable and susceptible of
application. If I have undertaken to write these few lines it is
because it has never been brought to my knowledge that up to the
present time the oxides and the alkaline salts of the earthy alkaline
metals have been studied from a photographic point of view.--_Leon
Degoix in Photo. Gazette._
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