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			cyanotype       G. L. Buffon Jardin des Plantes – Paris Cyanotype toned to tannic acid - ‘90s 12,5 x 19,5 cm.
	cyanotype (Blueprint)            Cyanotype is a photographic ‘direct blackening’ printing process born in 1840, using the very poor sensitivity of some iron salts that at the ultraviolet light changes their pale green colour to a strong blue, becoming in the same time insoluble into water.      The process do not need developer (the image is performed during the exposure) nor fixing agent (the same water removes the non-exposed salt). The advantages of the technique are mainly the easiness of making and the cheapness; disadvantages are: the very low sensitiveness (up to half an hour in bright sun), a tonal range rather poor and a scarce time resistance.      Besides that, the colouring does not fit any subject and for this reason special methods have been tried to change the colour, as the one using tannic acid that gives a more pleasant dark red. The name is still known as a way of reproducing tecnical drawings (no more in use).		Photogravure   Photogravure   Dichromated gum   Carbon process   Kallitype  Cyanotype   Silver print   Toning   BLACKHOLES  heliogravure 2006  WITH-DRAWN  heliogravure 2001  Questioni di Stile        - quotations