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

----- 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 

=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your 
account (the same e-mail address and password you set-up when you subscribed,) 
and unsubscribe from there.

Other related posts: