The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Cyanotype
The two latter solutions will keep several weeks. The solutions are mixed in the following proportions and order: -
Solution No. I.. ... ... ... ... 20 parts.
No. II............. 8 ..
.. No. Ill............. 5 ..
As soon as mixed this solution is thin, then becomes thick and cloudy, and then clear and liquid again, when it is ready for use. Well-sized paper is evenly coated with this solution with a broad brush, and the coating evened out with another brush. It must be quickly dried in a warm room, and protected from damp and light. In printing, the image appears as yellow on a darker ground. The developer is
Potassium ferrocyanide ... ... ... 20 parts.
Water           ............... 100 ,,
which should be spread over the proof with a broad brush, care being taken that no solution touches the back of the paper or stains will be produced. As soon as the image appears of a deep blue colour, the print should be well washed, and then laid in dilute hydrochloric acid 1 : 10 till the ground appears white; and the print should then be well washed and dried. Waterhouse has suggested another process.
I.
Gum Arabic............... 170 parts.
Water           ...............650 ..
II. Tartaric Acid           ... ... ... ... 40 parts.
Water           ... ............ 150 ..
III. Sol. ferric chloride 45 o Baume ... ... 150-120 parts.
Mix solutions 1 and 2, and add gradually, with constant stirring, No. 3 ; allow the mixture to stand for twenty-four hours, and then dilute with water till the specific gravity is itoo. The solution, and the paper sensitised with it, will keep for some considerable time. The exposure in direct sunlight is from 15 to 40 seconds, in diffused light from 10 to 30 minutes. As the image formed by light is only very faintly visible, it is advisable to use a strip of paper, either exposed under one corner of the plan or drawing, or under a similar and smaller one at the
170