A technical dictionary of printmaking, André Béguin.

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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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