Re: Cyanotype
With the traditional CyanotypeI don't believe anymore that there is a traditional or classical cyanotype. Here are the compositions in g/100 ml in sol A:B and their ratios, gathered from different sources: 12.5:4.5 = 2.78 Wall (Photographic Facts and Formulas, 1924) 24:7 = 3.42 Namias (Chimica Fotografica, 1929) 36:16 = 2.25 Clerc (La Technique Photographique, 1950) 25:12 = 2.08 Glafkides (Photographic Chemistry, 1958) 22:15.4 = 1.42 Nettles (Breaking the rules, 1977) 25:25 = 1.00 Frederick (Creative Sunprinting, 1980) 20:8 = 2.5 Barnier (Coming into Focus, 2000) Note that the ratio 25:12 (Glafkides) is very close to the optimal ratio Fe am. citrate/ferricyanide which gives the maximun yield in Prussian Blue. Higher values (an excess of fe am citrate over ferricyanide, requested for the formation of Prussian blue) give more sensitivity but also bleeding. Lower values (an excess of ferricyanide) give no bleeding, lower sensitivity and more contrast. DMax is proportional to the amount of Prussian Blue, so I suggest to choose a formula with a ratio equal or lower than 2.08, possibly increasing the overall concentration. Cyanotype is also very sensitive to alkalinity in the paper (most of them are buffered with calcium carbonate) and in the water, so a first soaking (not more than 30") in acidic water is higly recommended. Alberto
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