Re: Question for Ryuji toning silver/gelatin prints with sulfide toners

From: Stephen Tucker <digitalneg@hotmail.com>
Subject: Question for Ryuji toning silver/gelatin prints with sulfide toners
Date: Thu, 06 Nov 2003 15:00:04 -0500

> First, this is good news, eliminating the full wash sequence
> before toning is a huge time & resource saver. Would you
> please elaborate on how you discovered that this would work?
> Is stain elimination the principle reason for the usual “wash
> fully before toning” recommendation?

Yes, without sufficient rinsing, risk of staining is very
high. However, long washes that are required for permanence are
unnecessary before toning. Staining can occur by carryover of acid
from fixer, silver-thiosulfate complex ions from fixer, or other
possible chemical interference. By testing I have determined brief
rinses are sufficient to wash out these interfering compounds, but
this of course may depend on particular fixing bath, paper used and
washing water. If you see staining problems with 3 minutes rinse, I
would suspect if the fixing bath is exhausted or nearly so, if the
water is too acidic, etc. One way to minimize the risk is to use
carbonate bath before toning treatment. (All these apply to selenium,
sulfide, polysulfide or combination of these.)

> Second, is a residual hypo test such as Kodak HT-2
> a reliable wash indicator after using sulfide toners?

Yes, it is as reliable a wash indicator as without toning process.

Silver nitrate test for residual thiosulfate uses the reaction that
thiosulfate is capable of forming dark silver sulfide stain with
silver nitrate in acidic atmosphere. This reaction is not very
specific to thiosulfate, and it indeed detects thionates, which are
formed in print material by decomposition of residual thiosulfate
while drying and storing, if any, before testing. This is a good
thing, because thionates are also harmful to prints, and you'd want to
detect them. (Earlier residual hypo test failed on this one.) The
silver nitrate test is also sensitive to sulfide and polysulfides,
because these chemicals also react with silver nitrate to form dark
silver sulfide. This is not a bad thing because these are also harmful
if present in a large quantity, but if small amount of sulfide remains
in the paper fiber, the silver nitrate test would overestimate the
quantity of residual thiosulfate. So the result may err on the
conservative side.

There are a few technical issues with HT-2 test solution, so if you
are serious about quantitative estimation of residual hypo, I would
definitely recommend to study literature. ANSI PH 4.30-1962 is a three
stage version of silver nitrate test, but still has a couple of
technical issues. C I Pope published an improved method in
Photographic Science and Engineering in late 1960's. (will find
complete reference if anyone is interested -- I've been meaning to add
this topic to the web)

If selenium toner is used and selenosulfate residue is present in test
print, silver nitrate test would form similar dark stain but the
compound is, of course, not silver sulfide. The result may be biased
to the conservative side.

It is important to wash prints after toning even if the prints are
washed before toning, because toning baths contain thiosulfate,
sulfide, polysulfide and other sulfur compounds that you don't want to
stay in prints. (This applies to KBT, KRST, sepia toners, brown
toners, etc.) Sulfite after-bath is recommended (it's almost mandatory
to prevent stain and prevent over-toning) with polysulfide-containing
toners, and in this case, this bath doubles the duty as a wash aid.

Finally, I know Richard Knoppow would probably like to point out that
silver nitrate test should be used only after reasonable amount of
washing is given, because if too much thiosulfate is present, the test
may fail to detect residual thiosulfate.

--
Ryuji Suzuki
"Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)