A technical dictionary of
printmaking, André Béguin.
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"Printmaking dictionary"
PHOTOTYPE, COLLOTYPE,
ALBERTYPE
In 1855 A.Poitevin first thought of using bichromated
gelatine as a printing element by itself rather than
applying it on a lithographic stone (as had already been
done). C.M.Tissier du Motay and C.R.Marechal tried to
exploit this process commercially by using a copper plate
but it was not until 1868 that J.Albert of Munich perfected
the phototype process by coating plate glass with the
gelatine. His process came to be known as the Albertype.
Later on further improvements were made and the printer
G.Danesi even tried, with some success, to replace plate
glass with aluminium sheets which could be printed using a
rotary press.
Poitevin had noticed that
exposed areas of a gelatine layer had the property of
retaining greasy inks while the non-exposed areas tended to
retain water. Because of this characteristic some
lithographic techniques could be applied to
gelatine.
The process developed by
Albert worked as follows: mixed with potassium chromate the
gelatine was spread over a well scoured, grained sheet of
plate glass (* granulated plate surface, 3). Graining was
needed to make sure that the gelatine would "stick" to the
glass surface. After drying, the plate was first exposed on
the side opposite the one covered with gelatine (the
negative being turned around). As a consequence the gelatine
stuck very strongly to the glass surface. Then the gelatine
side was exposed, covered by the negative. Afterwards the
plate was washed to rid it of the excess bichromate. This
washing also caused the gelatine to swell in the non-exposed
areas proportionally to the amount of light received. The
surface of the gelatine layer reticulated immediately. This
slightly damp surface was then kept damp with a mixture of
water and glycerine. The inking of the plate was done
with a brayer and the printing was carried
out on a printing press capable of great
pressure.
Phototype impressions are
very fine impressions and, although not screened, respect
half tone values very well. However, the use of one plate is
limited to a maximum of one thousand impressions.
Furthermore, the workshops using this process must always
maintain a normal atmospheric humidity to ensure proper
results.
M.Vidal used the phototype
process in developing a colour equivalent process which came
to be known as heliochromy*.
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