From: Sandy King (sanking@clemson.edu)
Date: 10/26/02-07:59:32 AM Z
Brown ferric ammonium citrate is little used for vandyke because it
is much less sensitive than the green variety. You can see this
mentioned in the historical literature and recent observations appear
to confirm that this is indeed the case. However, if you want to
experiment with it anyway I would suggest three quick experiments: 1)
mix the vandyke chemistry using only brown fac, 2) mix it using only
green fac, and 3) mix is 50% green fam and 50% brown fac. Sensitize
three step wedges using each of the solutions and expose all three
for the same period of time. Then look at the contrast and printing
speed you get with each. This test should indicate whether there is
any use in continuing to work with the brown stuff.
On a related note I have used a combination of ferric citrate and
green ammonium ferric citrate to increase the contrast of vandyke
prints. This is the only way I know to really get more contrast from
vandyke. The other methods described in the literature . i.e. adding
a few drops of a potassium dichromate solution to the sensitizer, and
adding a few ml of a potassium dichromate solution to the developing
water, have absolutely not worked for me. I posted a message on this
a few months back and it should be in the archives.
Sandy King
>Does anyone know of a vandyke formula using brown ferric ammonium citrate?
>Or can someone estimate a ration of green to brown citrate for the standard
>formula ?
>
>Richard
>---
>Richard Urmonas
>rurmonas@senet.com.au
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