From: Monnoyer Philippe (monnoyer@imec.be)
Date: 07/25/02-09:42:50 AM Z
Sandy,
Very interesting.
It is indeed better to avoid adding acetic acid but only sodium citrate. Only one parameter at a time.
Though acetic acid is not strong enough (not a strong oxidizer) to bleach silver. But maybe it has, directly or undirectly, an inhibiting action. For example by introducing acetate in the solution ...
I am pretty sure that only sodium citrate helped dissolving the ferric citrate.
With the solution you are trying now (10g/10g), you will have mainly sodium ferric citrate in the solution + an exces of 1.67 g of pure ferric citrate. To have pure sodium ferric citrate, you should have added exactly 12.01 g of sodium citrate (assuming the you have sodium citrate under the form tribasic, dihydrate). The next test will allow you to find out what is the effect of changing ammonium into sodium in AFC.
If you look at the periodic table of the elements, you will see that in the sodium family you also have lithium, potassium, rubidium, cesium. If the next test gives you a clear change in contrast, then it's getting exciting.
You will probably be able to tune the contrast of VDB only by changing this ion, using
Sodium Ferric Citrate = Ferric Citrate + Sodium Citrate
Lithium Ferric Citrate = Ferric Citrate + Lithium Citrate
Potassium Ferric Citrate = Ferric Citrate + Potassium Citrate
Cesium Ferric Citrate = Ferric Citrate + Cesium Citrate
Ammonium Ferric Citrate = Ferric Citrate + Ammonium Citrate
...
Another way to control the contrast is maybe by tuning the ferric citrate/sodium citrate ratio, as long as it dissolves.
Staying tuned,
Philippe
PS: a bit more of silver nitrate might help to recover your Dmax ...
|-----Original Message-----
|From: Sandy King [mailto:sanking@clemson.edu]
|Sent: Thursday, July 25, 2002 16:26
|To: alt-photo-process-l@skyway.usask.ca
|Subject: Re: Ferric citrate in VDB formulas
|
|Philippe:
|
|OK, today the solution with sodium ferric citrate had cleared
|completely and I mixed up a VDB solution with ferric citrate and ran
|a comparison test of this solution with a classic VDB solution
|containing ammonium ferric citrate. Exposure of a Stouffer TP 45 step
|wedge was with BLB tubes for 10 minutes.
|
|Results:
|
|Classic VDB solution with AFC: First maximum black at Step 4, last
|visible step at Step 20, or a total scale of 18 steps.
|
|VDB with ferric citrate: First maximum black at Step 4, last visible
|step; at Step 17, or a total of 14 steps.
|
|Comments: The VDB with ferric citrate prints with the same speed but
|with much more contrast, about four steps or two full stops. The
|color is about the same, dark brown in both cases, but the maximum
|density of the classic formula appears to be just a bit higher. On
|the densitometer the maximum black of the classic formula with AFC
|reads 1.40 while the maximum black with the FC reads 1.34.
|
|I have just mixed a solution of 10g of ferric citrate and 10g of
|sodium citrate in 35ml of water, but without the acetic acid. It
|appears to be going into solution rather well so I hope to be able to
|avoid the acetic acid, which may have bleached the silver in the
|previous tests and caused the slightly lower maximum density reported
|above.
|
|Sandy King
|
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