From: Sandy King (sanking@CLEMSON.EDU)
Date: 09/23/02-01:08:01 PM Z
Bernhard wrote:
>Hi list,
>
>beside gum printing, cyanotype and carbon I am doing some
>experiments with VDB since a few weeks. Works fine, but
>unfortunately my exposure times are up to two hours with my regular
>UV light source (time for carbon printing for instance is around 10
>minutes using the same light source!) I found several notes in the
>literature concerning the use of the right modification of ammonia
>ferric citrate, which should be of the green form. On the face of it
>I' ve got the brown form ;-) which is assumed to print much much
>slower than the green salt. Does anybody have experience if speed
>might be improved using the green salt? And if so, how much faster
>could it be?
>
>thank you,
>Bernhard
The green form is definitely faster. All of the old books report this
and I have personally observed it in my experimentations with VDB in
an effort to control contrast. Carbon is indeed faster than VDB, even
with green ammonium ferric, but not nearly as much as you report. My
times with carbon (which are about the same as yours) are faster
than VDB with the green stuff by about a stop.
Sandy King
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