From: Sandy King (sanking@clemson.edu)
Date: 12/08/02-11:31:43 AM Z
Ed Buffaloe wrote:
>3% citric acid might be too strong for VDB. After 2 minutes each in 6
>successive trays of water with only a pinch of citric acid, I find that my
>VDB has become visibly less dense. Of course, it seems to gain much of it
>back in the fix...
I would expect some loss of density because acid bleaches the silver.
However, if the clearing baths are used after toning with gold,
platinum or palladium it is possible that there would be no fade back.
What I would propose as an alternative VDB processing procedure for
maximum image permanence would be this:
1. Expose the print.
2. Wash for a couple of minutes to get rid of most of the soluble
silver halides.
2. Tone.
3. Brief rinse.
3. 2 minutes in clearing bath #1 = 3% citric acid.
4. Brief rinse.
4. 2 minutes in clearing bath #2 = 3% citric acid.
5. Brief rinse.
5. 2 minutes in fixing bath #1 = 5% sodium thiosulfate
6. Brief rinse.
6. 2 minutes in fixing bath ##2 = 5% sodium thiosulfate
6. Brief rinse.
7. 2 minutes in 1% sodium sulfite solution.
8. Final wash of 30 minutes
This is obviously a much more complicated procedure than what is
normally used for VDB but in theory it should establish the acidic
conditions that would assure maximum elimination of residual iron
salts. Is this necessary to get image permanence? I don't know.
Richard Knoppow has provided information on how to test for residual
silver salts. Does anyone know how to test for residual iron salts?
Sandy King
>
>>
>> This is an interesting observation, and one that could explain why
>> with similar processing my VDB prints fog when exposed to strong UV
>> light, while kallitypes do not. The primary difference in my
>> processing procedures is that the kallitypes go through two separate
>> clearing baths of 3% citric acid, a step that is omitted in
>> processing VDB. If this difference alone explains the fog then it
>> would appear to result from residual ferric oxalate, not residual
>> silver salts.
>>
>> Two questions. First, I wonder what would happen if one followed Ed's
>> clearing procedure but carried it out in the conditions I described,
>> afternoon shade where there would be still a lot of UV light. Second,
>> has anyone tried to process VDB using Kallitype clearing procedures?
>> I suspect that the use of a citric acid clearing bath before fixing
>> would bleach the image quite a bit, but perhaps if the clearing was
>> used after toning there would be no bleaching?
>>
>> Sandy
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