These can be produced by what is known as the powder or dusting-on
process. The principle of the process is this: An organic, tacky
substance is sensitized with potassium bichromate, and exposed under a
reversed positive to the action of light. All the parts acted upon
become hard, the stickiness disappearing according to the strength of
the light action, while those parts protected by the darker parts of
the positive retain their adhesiveness. If a colored powder be dusted
over, it will be understood that it will adhere to the sticky parts
only, forming a complete reproduction of the positive printed form.
Prepare--Dextrine, one-half ounce; grape sugar, one-half ounce;
bichromate of potash, one-half ounce; water, one-half pint: or
saturated solution bichromate of ammonia, 5 drachms; honey, 3
drachms; albumen, 3 drachms; distilled water, 20 to 30 drachms.
Filter, and coat clean glass plates with this solution, and dry with a
gentle heat over a spirit lamp. While still warm the plate is exposed
under a positive transparency for from two to five minutes in
sunlight, or from ten to twenty minutes in diffused light. On removing
from the printing frame, the plate is laid for a few minutes in the
dark in a damp place to absorb a little moisture. The next process is
the dusting on. For a black image Siberian graphite is used, spread
over with a soft flat brush. Any colored powder can be used, giving
images in different colors. When fully developed the excess of powder
is dusted off and the film coated with collodion. It is then well
washed to remove the bichromate salt. The film can, if desired, be
detached and transferred to ivory, wood, or any other support.
If a black support be used, a ferrotype plate on Japanned wood, for
instance, pictures can be made from a negative, but in this case a
light colored powder must be used. The Japanese have lately succeeded
in making some very beautiful pictures in this manner. Wood is coated
over with that black enamel for which they are so famous, and pictures
made upon it in this manner. They use a gold or silver powder.
With this process an almost endless variety of effects can be
obtained. For instance, luminous powder can be employed and an image
produced which is visible in the dark.
Some time ago we suggested a plan of making what might be termed
"post-mortem" photographs of cremated friends and relations. A plate
is prepared from a negative of the dead person in the manner
described, and the ashes dusted over. They will adhere to the parts
unexposed to light, and a portrait is obtained composed entirely of
the person it represents, or rather what is left of him. The idea is
not particularly a brilliant one, nor do we desire to claim any credit
for it, but we give it here for the benefit of those morbid
individuals who delight in sensationalism, and who purchase and
treasure up pieces of the rope used by the hangman.