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			dichromated gum       From SMEMBRA portfolio multiple gum printing 25,8 x 38,8 cm. - 1998
	dichromated gum            The dichromated gum process or simply ‘gum’ (socalled on account of the use of the vegetable rosin ‘arabic gum’ colloid instead of the photographic animal gelatine), was born about 150 years ago and has been largely successful for at least 40 years. Often it had a revival and to day is probably the most popular technique for experimentation, among the obsolete photographic processes. The success is due to the simple way of procedure in comparison to others and the endless expression’s possibilities permitted both in addition or in subtraction on the copy.      The best drawing paper – better if suitably prepared - is spread with a rather thick solution of arabic gum in water, coloured with a pigment and ‘salted’ to be sensitized. The dry sheet is exposed under a negative continuous tone film, to create the positive image through the tanning (hardening) of the jelly proportionally to the amount of light it received. The unhardened (or partially hardened) matter, will dissolve into water, carring away the surplus pigment while leaving the image grasped at the paper.      The process – and all the variants as ‘multiple gum’ that uses differents layers of coloured gum ‘in register’ – permits really acrobatic interpretations and a much better tonal range, but planned results need great deftness and good exercise.		Photogravure   Photogravure   Dichromated gum   Carbon process   Kallitype  Cyanotype   Silver print   Toning   BLACKHOLES  heliogravure 2006  WITH-DRAWN  heliogravure 2001  Questioni di Stile        - quotations