Hi Henk,
no color changes till now and my oldest toned cyanotypes are some years old -- Iīm pretty new in this business. At the end tannic/gallic acid toning causes the forming of ferric tannate/gallate which is document proof ink prescribed for writing and signing every treaty since 13hundred-anything. So I donīt expect bad surprises if the prints remain dry and the material for archiving is unbuffered and acid free. Otherwise the color tone could change from warm to cool (ph lowered) or cool to warm (ph heightened) in a very short time. This may be used to make prints changing their color in a certain degree over the times. To prevent this a neutral ph buffer would be appropriate.
All the best
Kai
Received on Sun Nov 13 11:38:04 2005
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