Tartaric Acid as contrast agent in VDB?

From: Sandy King ^lt;[email protected]>
Date: 01/03/04-10:31:21 AM Z
Message-id: <a06020428bc1c9c7b85b8@[192.168.1.100]>

Loris,

It has been some time since I did any VDB printing but tests I did a
couple of years ago in increasing the amount of tartaric acid in the
sensitizer in an attempt to increase contrast indicate that it did
not work. As best I recall sensitivity was decreased but actual
contrast (as evaluated by the actual exposure scale of the print as
judged by the results of printing a 21 step tablet) did not change at
all. So, the practical consequence of adding the tartaric acid may be
just an increase in printing times, which could explain, at least in
part, why your exposures appear to be so long.

Sandy King

> > However, 8-10 minute exposures seem incredibly long to me for digital
>> negatives, considering your set-up, i.e. high output tubes used at 3"
>
>I agree. It's long. As you make this remark I realized that my Van Dyke
>chemistry is not standard:
>
>Solution A: 27gr Ferric Ammonium Citrate + water to make 100ml
>
>Solution B: 6gr Tartaric Acid + water to make 100 ml (the standard formula
>is 4.5gr)
>
>Solution C: 12gr Silver Nitrate + water to make 100ml
>
>As you can see the amnt. of Tartaric Acid is 50% more than the standard (to
>increase contrast). Can be this modification causing the speed loss?
>
>> from the printing frame with close spacing. My set-up for the tests
>> described in my article on UV light sources was normal output bulbs
>> used at about 4" from the printing frame. Also, as you can see from
>> the tests the first maximum black is at about Step 3 or Step 4,
>> indicating that the tests received about 1.5 to 2.0 stops more than
>> needed. And these results pretty much agree with my current work
>> conditions as typical exposures for VDB and kallitype with my bank of
>> BLB tubes is in the 2-3 minute range for digital negatives with a UV
>> printing density of about 1.8 (from about 0.20 to 2.00).
>
>One more interesting fact is that if I vary the exposure considerably
>results don't change by the same proportions. For instance once I tried 8,
>12 and 16 min. exposure with the same lith negative and only midtones and
>highlights were affected - highlights more; as if the emulsion was self
>masking? What can be your comments for this phenomenon?
>
>Regards,
>Loris.
Received on Sat Jan 3 10:35:21 2004

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