- The collotype is a printing process in fat ink, the main characteristic of which is its possibility of reproducing images in halftone without weft, what distinguishes it from all other current processes of printing office.
- The process based on the property which possesses the bichromatée gelatin when it is insolée with an ultraviolet light to modify its internal structure. The consequences of this modification are characterized by a possibility of inking on the insolées parts (in principle through a photographic negative), and an aversion of the ink on the parts not irradiated of the coat of gelatin, which remain wet during the operations of printing.
- The various phases of the process are the following ones :
- Preparation of plates :
- We assure the good adhesion of the dichromated gelatin to the plate with interposing a first preparation.
- We put down the sensitive coat (gelatin + water + bichromates alkaline) which is dried in drying oven.
- Exposure :
- It is made in a frame, under a negative, with a diffuse ultraviolet light.
- We wash then in the cold water the plate to make clear alkaline salts.
- We let dry naturally – the plate is ready for the printing.
- Printings :
- The plate is arranged flat and then wetted with a mixture of water and glycerine.
- It is then cleared of this solution.
- We proceed to the inking of the plate by means of a roller. The ink is retained in the parts insolées by the image, proportionally in the quantity of received light, by letting appear all the range of the halftones, with an incomparable precision !
- It is then enough to apply the paper sheet intended to receive this ink which establishes the image, by means of a press.