[pure-silver] Re: Selenium toning + Agfa Sistan

When using Sistan, I'm never quite sure what the proper technique for 
wiping off excess is. What's the recommended procedure? Sponge, coffee 
filter, shake???

Thanks -
Malcolm


On Nov 25, 2004, at 7:26 PM, Richard Knoppow wrote:

>
> ----- Original Message -----
> From: "DarkroomMagic" <info@xxxxxxxxxxxxxxxx>
> To: "PureSilverNew" <pure-silver@xxxxxxxxxxxxx>
> Sent: Thursday, November 25, 2004 4:11 PM
> Subject: [pure-silver] Re: Selenium toning + Agfa Sistan
>
>
>> We may never get the complete story (Agfa doesn't have a
>> research staff
>> anymore either), but they are talking about Sistan working
>> on silver salts
>> produced through oxidation in the print's future.
>> Remember, Sistan is
>> applied to the print and should not be washed out
>> afterwards. It is staying
>> in the print to work on future silver oxidations, turning
>> them into
>> insoluble silver compounds. The text says that these
>> compounds build the
>> protective layer at that time.
>>
>> Selenium and KBT will protect the silver from this
>> oxidation by forming mor=
>> e
>> stable silver selenide and silver sulfide, respectively.
>> Hence, Sistan has
>> nothing to do work on in a fully toned print. However,
>> these toner
>> conversions are never 100%, and that's why I like the
>> Sistan treatment in
>> addition to toning.
>>
>> IMHO, Sistan is not a replacement for toning as this
>> brochure promotes. The=
>> n
>> again, using Sistan without prior toning is better than
>> using no print
>> protection at all. However, there are arguments that
>> Sistan might not be
>> needed if the print has been toned. I just like to be
>> sure, and Sistan
>> cannot hurt as a final treatment, if its residue is wiped
>> off.
>>
>>
>>
>>
>> Regards
>>
>>
>>
>> Ralph W. Lambrecht
>>
>>
>>
>    Sistan consists of Potassium thiocyanate and a wetting
> agent (Triton-X). Thiocyanates were used as a stabilizer in
> the old stabilization rapid processing system to prevent
> decomposition of the halides left in the emulsion. I think
> the function must be similar in fixed and washed prints. I
> suspect the action is similar to that of a small residue of
> thiosulfate in the emulsion. That apparently operates by
> creating about a one molecule layer thick coating of silver
> sulfide on the image silver. Silver sulfide is very stable.
> It may have other functions, Agfa has never been very clear
> about the theory behind it. Fujin makes a similar stabilizer
> called Ag-Guard. This is not Thiocyanate, I don't know what
> is in it. Fuji's published research shows Ag-Guard to be
> effective in protecting silver images against oxidation and
> sulfiding but not as effective as toning with a sulfide
> toner.
>    Its difficult to figure out what, if any, effect Sistan
> or Ag-Guard has on toned images because there is no
> published theory and there is no research data whatsoever. I
> think both are useful where some protection is desired
> without changing the color or density of an image but for
> genuine archival lifetime sulfiding toners of the
> Polysulfide type seem to be the best choice.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx

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