Year: 1876

ENGRAVING BY SUNLIGHT ON aELATINE


HELIoTYPE PRINTING.


Since the discovery Of photography, il
has been the dream Of many to utilize it in
connection with printers ink. Some Of
these dreams have had realization. In
New York leading firm Of toy book pub
fishers do their whole engraving through
the agency of photography and the acid
bath. In their establishment any object
that can cast shadow or be photographed
can be put in. printers ink. They run
thirteen Campbell presses steadily the
year around on this kind Of work.


The heliOtype process is probably the
greatest achievement Of the nineteenth CEN
tury in the art of applying printers ink.
of all the processes it is the rudest, and
while the rudest the most delicate in its
result. We do not propose to give tech
nical and minute detail Of the process, but
will describe the process as it is seen in
practical operation in the Office of 0sgood
Il Co., Of Boston.


The paraphernalia of the Office consisted
of several old, dilapidated hand presses,
loose in every joint, and, to all appear
ances, useless, except for the heliotype pro-
cess, for which age had apparently adapted
them. With these there was the ordinary
dark room Of the photographer a few
sheets Of glass of large size, also several
plates of sheet iron ground on one side.
To each press there were two ordinary
hand rollers, glass distributing slab, a
bowl and sponge, and an instrument called
squeegee "a rubber scrapcr.) : The oper-
atives were day laborers, taught to go
through certain routine which produced
the most exquisite pictures, over which
they had no control except to get off 150
impressions per hour.


The first operation, after getting good
sharp negative by photography or other
wise, was to print from this on sheet Of
gelatine, prepared by combining gelatine,
bichromate Of potash and chrome alum 10
certain proportions. The action of the
light literally engrayes the object in this
gelatine, the most delicate graded tint be-
ing as absolute as the strong, deep colors.
When the light has acted sufficiently to
produce the desired result, the gelatine is
soaked in cold water to remove the super
Huous chemicals. When this is done, the
form is ready to go to press.


Having immersed in clean water the
sheet iron plate, about FIVE inches larger
each way than your gelatine, you proceed
to place the gelatine in the centre of this
plate, while under water When done
you lift them out and with the squeegee
expel. the water from between them, and
then fasten the edges down with strips Of
prepared paper, and then remove the
surplus water by several layers of blotting
paper. The form is then technically rolled
up; that is, the engraving is filed with ink
by skilled workman. When II is so done
it is ready for the press.


The press work is as follows The iron
plate, with its gelatine form, is placed in
the centre Of the bed. 1t is raised type
high, and secured in its place. A mask
or frisket is used, as in ordinary printing,
except it is of parchment or of oiled paper.
The gelatine has the property of resisting
water where the light has acted on il, aud
absorbing where the light has not touched
it. consequently the faintest touch Of the
light is readily printed. These are the
parts that take the ink, because they are
dry, the wet portions resisting it, as in the
ordinary lithograph. Upon these peculi-
arities of the gelatine are based the whole
process


The form is wet with sponge, and the
surplus scraped off with the squeegee and
blotted once, after which from ten to
twenty-five impressions can be taken with
out re-wetting. The workman first rolls
up his form with an excess of ink. He
then uses second roller, removing all the
ink possible from the form. If he has
used tinted water to damp his form, his
tympau will give distinct outline, and
his work will have an appearance as If
printed on delicate background. If
heavy ink is first used, then light thin
ink and tinted water for damping, a pic
ture will be produced with sharp, well.
defined foreground, while the shadings
and tinting will be softer aud more deli
cate than is possible by the camera.