Picked white Gum Arabic 75 grains
Bromide Ammonium 200 "
Gelatine 150 "
Water 10 oz.
Nitrate of silver 300 grains
Water 7-1/2 oz.
Dissolve in two jars in a vessel of water heated to 140 degrees F.,
stir each solution well with a separate rod or strip of glass, and
when equally heated to 140 [p042] degrees the silver may be
poured in a gentle stream into the gelatine gum solution by the aid
of a safe light.
When all has been mixed and thoroughly stirred, cover the top of the
dish and allow the temperature to be at 140 degrees for eight hours,
occasionally stirring the emulsion during that time, which should be
done in the dark.
At the end of that time there should be weighed out, of Nelson's
soft gelatine 250 grains, and of French hard gelatine 150 grains.
This 400 grains of gelatine must now be added to the emulsion, and
occasionally stirred until all of it is thoroughly dissolved and
incorporated with the emulsion, which will take about a quarter of
an hour; it is then poured out in a clean 12×10 deep porcelain dish
to set, and should be allowed to set for forty-eight hours, when it
may be wrung through a piece of coarse canvas and allowed to fall
into a solution of
Common salt 1/2 lb.
Water 1 gallon
Let it remain in this for five minutes, then strain through a horse
hair sieve and wash it well for an hour and a half. Allow the
shreddy emulsion to drain well in the sieve for about a quarter of
an hour; at the end of that time place it in a clean stone-ware jar
to melt, with the addition of four drachms of saturated solution of
nitrate of potash upon melting, which may be done by setting the jar
into a dish of water at a temperature of about 120 degrees F.
It will be found on measurement to be nearly 25 ounces of emulsion;
as soon as it is ready for filtering four ounces of methylated
spirit may be mixed with it, [p043] to which have been added four
drachms of an alcoholic solution of tannic acid, made by mixing ten
grains of tannic acid with one ounce of alcohol; this is to prevent
frilling.
The rapidity of the plates will be about eight times that of a wet
collodion plate, which for all ordinary purposes will be as rapid as
could be desired.
Dr. Eder, the distinguished German scientist (who is a great
authority on gelatine emulsions, and has published a book on this
subject), gives the two following formulæ:
GELATINE EMULSION. C.
EDER.
Bromide potassium 4 grams, equal to 61 grains.
Gelatine 7-1/2 to 8 grams, " 115 "
Water 50 c. c. " 1 ounce.
Nitrate of silver 5 grams, " 77 grains.
Water 50 c. c. " 1 ounce.
Dissolve the silver in water and precipitate it with ammonia.
Continue the addition a few drops at a time, until the brown oxide
of silver re-dissolves and the liquid looks as bright as pure water;
the strength of the ammonia is immaterial.
The nitrate of silver may be warmed to 93 degrees F., and poured
into the bromized gelatine a little at a time, continually stirring
with a glass rod. Rinse the silver bottle with 10 c. c. about 1-1/2
drachms of water and add it to the emulsion, place the bottle
containing the emulsion in a basin or saucepan of water heated to 90
degrees F., leave it therein from 15 to 30 minutes without further
heat; after 30 minutes the emulsion is ready to be congealed
previous to washing.
This emulsion never fogs, but it is imperative that [p044] in no
part of the progress the temperature should exceed 100 degrees F.,
and it is a safe rule not to go beyond 90 degrees F. It is
recommended to use French gelatine.
GELATINE EMULSION. D.
EDER.
Bromide of potassium 61 grains.
Gelatine 115 "
Water 1 oz. (plus)
The bromide of potassium must be pure and not alkaline, ditto the
gelatine.
The bromized gelatine must be melted at 140 to 160 degrees, and then
add 77 grains of silver nitrate in one ounce (plus) of water. The
silver may be warmed to the same temperature as the gelatine, but
this is immaterial. Rinse the silver bottle with three drachms of
water and add it to the emulsion. The bottle with the emulsion is
now put in a saucepan partly filled with hot water, covered to
exclude all light, and the water in the saucepan set boiling, which
should be continued for 25 to 30 minutes, then both water and
emulsion cooled down to 90 degrees F., then add 340 minims of
ammonia, stirring it thoroughly through the emulsion, which should
be left for from 30 to 40 minutes at a heat of 90 degrees F., then
it is ready to set and wash.
Dr. Eder says this last is quicker and better for portraits.