[pure-silver] Re: Hypo Eliminator
- From: Ryuji Suzuki <rs@xxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 18 Feb 2005 02:22:47 -0500 (EST)
From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
Subject: [pure-silver] Re: Hypo Eliminator
Date: Thu, 17 Feb 2005 23:02:43 -0800
> Kodak was evidently aware of this problem and suggested
> that Potassium bromide be added to the eliminator to prevent
> the color change to the image. There are other problems with
> hypo eliminator so it has not been recommended for a couple
> of decades. A sulfite wash aid is quite sufficient.
I think the reason bromide was added is because hypo eliminator was
found to be ineffective unless bromide is added. Forgot details but
have papers somewhere. It's also described in James, either 3rd or 4th.
> Staining from KBT _may_ be from unfixed halide but it
> also can cause a stain if its not stopped with a 10% sulfite
> bath after toning and before washing. Polysulfide toners
> have the peculiar property of toning faster as they become
> diluted or exhausted. When you put a toned print in the wash
> it will continue to tone at an accelerated rate until the
> toner is washed out. Washing must be very rapid at the
> beginning. A "stop" bath of 10% sodium sulfite (about stock
> KHCA) will prevent the continued toning and staining. The
> print must be treated in this for a couple of minutes before
> washing. I don't know the chemical basis of this but it
> seems to happen.
I bet the staining Peter is talking about is not that. He's been
around for a while and he must've heard this 25 times. There are some
staining with polysulfide toners that occur with some paper but not
others, both perfectly fixed and rinsed.
High silver load in the fixer can also stain prints. When silver
loaded fixer is mixed with polysulfide toner in a test tube, black
precipitate forms. But when fresh ammonium thiosulfate is mixed in a
test tube, nothing forms. (Both are done at a ratio that does not
cause elemental sulfur precipitation.)
--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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