IMPROVEMENTS IN THE PREPARATION OF PRINTING SURFACES IN PHOTO-MECHANICAL PRINTING
Year: 1870

page_text: PROVISIONAL SPECIFICATION left by John Robert Sawyer at the
Office of the Commissioners of Patents, with his Petition, on the
19th November 1870.
I, JOHN ROBERT SAWYER, of Norwich, in the County of Norfolk,
do hereby declare the nature of the said Invention for "IMPROVEMENTS
IN THE PREPARATION OF PRINTING SURFACES IN PHOTO-MECHANICAL PRINTING," to
be as follows:-
This Invention is based upon the well-known property possessed by
gelatinous and albuminous matters when mixed with bi-chromate salts
of being sensitive to the action of light, of being rendered soluble or
insoluble in water according to the degree of intensity of the light, and
on the property possessed by such compounds of receiving or rejecting
the ordinary commercial printing ink in accordance with such solubility or
insolubility in water.
My Invention relates to improved methods of obtaining printing
surfaces, by which not only is the most delicate detail light and shade
of an ordinary photograph preserved, but any writing, lettering, drawing,
addition, or alteration may be made, and the surfaces so prepared,

page_text: printed from either by hand or mechanical power in the ordinary
lithographic or copper-plate printing press, and with extreme rapidity,
using the ordinary lithographic inks in all colors and shades.
In carrying my Invention into effect I proceed as follows:-Upon a
surface of metal, stone, enamel, glass, porcelain, or other suitable
material, I place a layer of gelatine dissolved in water, to which has
been added a certain quantity of the bi-chromates of ammonia or
potassium, either separately or mixed together. This layer is dried by
hot air and kept perfectly level during such drying, it is then exposed
under a negative to the action of light. When the image can be
perfectly made out, and the high lights are on the point of turning
brown, the plate is removed from the light and placed for one hour in a
dish of cold water which is changed three or four times during that
period, it is then removed, well washed under a tap, and allowed to dry
and harden in a temperature of from 80 to 100 degrees Fahrenheit. The
plate after a lapse of forty-eight hours or more is then placed upon the
carriage of an ordinary lithographic press, the bed of which is fitted
with a piece of soft wood of the size and thickness of the largest litho-
graphic stone the press will take, the plate being kept in its place by
wooden studs which drop into holes made in the wood, and which are
a trifle lower than the plate itself. I then damp the plate with a soft
sponge, allowing the gelatine to imbibe as much water as possible. I
then surface dry it with a very fine soft cloth and proceed to roll in with
an ordinary ink roller retransfer ink such as is used in the ordinary
transfers of plate to stone, or stone to stone. When the ink appears to
have properly permeated all the delicate lights and shades of the image
I place upon the plate a piece of transfer paper, coated or not coated
according to the ultimate effect desired. Upon this I place five or six
sheets of fine soft paper, fold down the tympan, and after adjusting the
pressure carry it beneath the scraper of the press, the paper is then raised
very carefully from the gelatine surface, and if the print is entirely perfect
is ready for the next operation, which is as follows:-The picture, cut to
the exact size and shape it is desired to be when finished, is damped by
being placed between damp blotting paper. In the next place a polished
lithographic stone warmed to a temperature of about 100 degrees
Fahrenheit is placed upon the bed of an ordinary lithographic press
accurately adjusted and levelled; the before-mentioned damp print is
then placed in the required position on the stone, on which any writing,

page_text: lettering, or design may have been previously added either by writing or
lettering on the stone or by the ordinary mode of transfer. The print
being in its proper position is then covered with soft paper, the pressure
adjusted, and the stone is passed several times through the press. The
back of the print, which now adheres to the stone, is next sponged with
water, the stone turned and passed through the press in an opposite
direction, after which the back of the print is softened with water and
gently rubbed with the fingers until the paper can be easily removed from
the stone. The impression is then gummed and inked up like an ordinary
lithographic transfer, and if the design or writing has not been previously
added to the stone, it may now be added. The image on stone may
be strengthened, weakened, or modified by touching up or erasing, and
when considered satisfactory the whole may be printed in the usual way,
either by hand labor or mechanical power.
The operation thus described is suitable for prints produced from hard
surfaces such as glass, porcelain, enamel, stone, or wood, but another
method which I use is effected as follows:-I prepare paper with
gelatine and lampblack (or obtain it ready prepared of the Patent
Autotype Company, whose license I hold); such prepared paper or tissue
I float on a solution of bi-chromate of potash which renders it sensitive
to the action of light, and when dry it is exposed under a negative
for the necessary period; I then immerse this tissue, bearing the latent
image, in cold water, and when softened and rendered limp I lay it face
downwards in the proper position on a polished lithographic stone, or
on plate glass which has been previously coated with a mixture of
albumen, gelatine, and bi-chromate of potash, making it adhere firmly
by means of an instrument called a "squeegee." I then immerse the
stone or glass face downwards in water of a temperature of about 120
degrees Fahrenheit, this in a short space of time removes the paper
and the surplus gelatine and carbon, leaving the picture in all its delicate
lights and shades upon the stone or glass. I then proceed to add any
writing, lettering, or design as before described, roll in with litho-
printing ink, and work off in an ordinary press. Sometimes I find it
advisable not to transfer the prepared tissue after its exposure under the
negative at once to the stone or glass, in such cases I coat the face of it
with a solution of india-rubber in benzole, and place it face downwards
on a piece of paper also coated with the india-rubber solution, making
the two adhere perfectly. On placing it in warm water the paper upon

page_text: which the gelatine and carbon originally was soon floats off, and the
picture begins to develop by the removal of the surplus gelatine and
carbon. When the picture is complete and satisfactory I cut it to the
proper shape and size, lay it upon a polished lithographic stone or on
plate glass previously coated with a mixture of albumen, gelatine, and
bi-chromate of potash, press it into intimate contact, and when dry
remove the adhering paper by means of benzole; the drawing so placed
on the stone is then ready for inking and working, as before described.
It occasionally happens that it is necessary to print only a small
number of copies, and in that case it is desirable to print them from the
original gelatine film; the difficulty has heretofore been to render that
film sufficiently hard and tough to enable any number of copies being
obtained from it, and many ways have been suggested of mecting this
difficulty. I find that a spirituous solution of a hard gum or lac, by
preference white lac, answers the purpose entirely, other hard gums may
however be used. I add ten grains of best white shell-lac dissolved in
half an ounce of strong spirits of wine to each pint of gelatine mixed
with the bi-chromate salts, the aqueous solution will at once precipitate
the gum if the solution containing it is not added carefully a little at
a time, but if this precaution is taken, and the mixture is vigorously
stirred during the addition, sufficient of the gum will remain in the
gelatine to render the resulting film exceedingly hard and tough, and
perfectly capable of yielding several hundred copies.