Collotype

12 October 2010 § Leave a comment

 

Collotype by Josef Albert, 1868

 

Collotype (Dutch: collotypie or lichtdruk, French: Phototypie, German: Lichtdruck) is a printing-technique of which the underlying principle was discovered by the Frenchman Louis Alphonse Poitevin (1819-1882) in 1854. He patented his technique, under the name ‘photo-lithography’, in August 1855. The name collotype derives from the Greek kólla, meaning glue.

Method and machinery

Collotype is a form of planographic printing, based on chemical principles. Printing can be done manually, but also machine. For making collotype one needs gelatin mixed with bichromate; the bichromate is necessary for making the gelatin react to light. This mixture of gelatin and bichromate is put on a plate of either glass or metal and is left to dry in an oven at 50 °C. During this drying tiny curving cracks appear in the gelatin-layer; these cracks will appear on the eventual print, but are so small that they cannot be distinguished with the naked eye (this structure is called ‘Runzelkorn’ in German).

It is a known characteristic of gelatin that it will swell under the influence of cold and dissolve under the influence of hot water; however, when bichromate is added, this reaction will take place very quickly when the gelatin is under the exposure of light, and very slowly when it is not. The result is that, when a non-rasterized photographical negative is projected on the gelatin, the parts that remain dark will stay soft and hydrophilic, while the parts that have been illuminated will harden and become hydrophobic.

When the image is fixed to the gelatin, it is rinsed with water to which is added glycerine, to keep the surface humid. On the hydrophilic parts the water will cling to the surface, on the hydrophobic parts the water will recede, thus making the dry and harder parts receptive, the humid soft parts non-receptive for ink (plus of course all gradations of humidity in between; making parts that are somewhat receptive for the ink) The ink is absorbed to a bigger or lesser degree by the small cracks in the gelatin. The difference between lighter in darker parts of a collotype-print is not caused by receding darkness, or in other words getting lighter or grayer of the ink itself, but by a receding quantity of lines; the few lines that are visible even in a light part of the print are equally dark as the lines in a dark part – only there of course are more lines to be seen (this is also one of the features which makes collotype distinguishable from aquatint, however these differences can only be seen through a microscope).

History

The difference between the collotype as we know it and the ‘photo-lithography’ as patented by Poitevin is as follows: Poitevin used exactly the same technique as described above, but added an extra step to the process; when the ink was absorbed by the gelatin, he made an offprint on a stone, and printed on paper from the stone. Even though a good result (perfect toning and being able to print 2.000 copies) with collotype was achieved by F. Joubert, a French engraver in 1860 (he published a portrait in The Photographic Journal), he never unclosed his ways of getting that good a result, and no one bought the rights from him when he offered them.

In 1868 at least two people independently were working on the ‘photo-lithography’ that Poitevin discovered; Albert Husnik in Prague and Joseph Albert (the eponym of the albert(o)type; a technique used from 1870 to print colored collotypes); both found out that it was not necessary to offset the gelatin-print on a stone before printing it onto paper, but that it was possible to use the gelatin itself as printing form. Also they both came up with ways to make the gelatin more adhesive to the underlying glass or metal plate. We read in Van Der Linden (1979,195) that these two men started working together from a certain point, but Gernsheim & Gernsheim (1955,268) tells us that Albert removed competition from the market by buying Husniks technique from him.

Collotype was a popular technique for photographical printing for a long time; Gascoigne (2004, 40) lets us know that the last collotype-press in England closed down in 1983. In the 19th and 20th century collotype was used for many types of printing; reproductions of drawings, watercolors and print in art-books (it is said that collotype was not suitable for reproducing oil-paintings), for postcards or for scientific pictures in which a large accuracy was needed. Collotype probably became popular because it was a relatively easy technique with high quality results; also, in the time of its discovery there was a high demand for photographic pictures. [Joëlle Terburg]

Bibliography:

Contemporary:

Husnik, J., Das Gesamtgebiet des Lichtdrucks, A. Hartleben, Vienna, 1885.

Monet, A.L., Procédés de reproductions graphiques appliquées a l’imprimerie, Administration du ‘bulletin de l’imprimerie’, Paris, 1888, pp. 223-236.

Modern:

Gascoigne, B., How to identify prints, Thames & Hudson, London, 2004, pp. 40-41.

Gernsheim, H. & Gernsheim, A., The history of photography, Oxford University Press, London, 1955, pp. 367-368.

Linden, F. van der, De grafische technieken, Cantecleer bv., de Bilt, 1979, pp. 194-196

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