Since the introduction of the new process into the United States,
the preparation of rapid dry plates has been and remains now in the
hands of certain prominent firms, who, from the skill they have
acquired and the advantages they derive from all the machinery and
conveniences that large capital enables them to procure, are enabled
to supply fully the demand with a much better article than could be
had were each consumer to manufacture for himself. In fact, if the
photographer were compelled to manufacture his own dry plates there
would be a very different condition of affairs at the present time.
Gelatine is a substance so susceptible to change from the action of
our climate, with its varying temperature, that of a large number
who have attempted to make dry plates for the trade, many have
completely failed, some of them after a partial success; and others
after spending thousands of dollars never could make two batches of
emulsion alike; and then again the keen competition of the
successful concerns has reduced the profits to not more than fair
returns to a precarious business.
There are many, no doubt, who would be glad to experiment in this
field, especially among amateurs, and it is for the benefit of such
that certain hints and formulæ are given in this connection to
enable them to make, if successful, their own plates.
The formulæ herewith given are selected from a large number
published in the German, English and American journals, and while
good dry plates may be made by either of them, yet it is doubtful if
the highest success would repay the outlay. [p039]
A careful study of the published formulæ and the current literature
on the subject of Gelatino-Bromide Emulsion will disclose the
general principles on which they are based.
A certain amount of bromide of ammonium or potassium (preferably
ammonium, on account of its greater uniformity and purity) and
nitrate of silver are dissolved separately, and mixed together in a
thin solution of gelatine, at a moderately warm temperature. Great
sensitiveness is obtained by a long exposure to the same warm
temperature, or by the addition of a small amount of ammonia, and
raising the heat to the boiling-point for from a half to a full
hour; when it is cooled more gelatine is added and the whole allowed
to congeal or set, when it is reduced to shreds, and washed in cold
water to remove the excess of the preponderate salt.
The sensitiveness of the emulsion is said to depend upon the
fineness of sub-division of the grain of the bromide of silver in
the presence of the gelatine. This extreme fineness is secured by
long emulsification, or by the use of ammonia and a boiling heat.
The strength and tenacity of the emulsion depend on the quality of
the gelatine, and its freedom from deterioration during the process
of emulsification and the subsequent washing. A soft gelatine is
suitable for the process of emulsification; afterwards a hard
quality is used to give body and resistance.
The presence of free bromide or of free nitrate of silver in the
finished emulsion would be fatal to its usefulness; therefore, as
both of those salts are easily soluble in water, they must be got
rid of by washing; consequently, before washing, the mass of jelly
should [p040] be induced by the use of a refrigerator to set firm
and hard, so that it may be broken up into shreds for washing, and
the smaller the shreds the less washing they will require.
Of the following formulæ the first two are copied from English
photographic year books, and are believed to be reliable; the others
are by Dr. Eder, the greatest German authority on gelatine emulsion,
and they are comparatively simple.