Francis
>The bottom line is do not use buffered matboard with cyanotype. Also watch out
>for buffered paper boxes and paper that might come in contact with cyanotype
>prints. Buffered materials are used so that the base incorporated will help
>neutralize the acid which forms from lingum in the paper and/or acids that
>come from sulfer dioxide in the atmosphere. The base will bleach the cyanotype
>prints. It may take a while, but eventually it will, especially if the
>humidity
>is over 40-50 %. I have been told that Rives BFK is buffered so every time I
>buy a new batch, I check its pH. Why bother with buffered matboard. Why not
>use a good grade of acid free matboard for everything?
>
>Bob Schramm