[pure-silver] Re: When is Sulphide toner not sulphide toner?

----- Original Message ----- 
From: "DarkroomMagic" <info@xxxxxxxxxxxxxxxx>
To: "PureSilverNew" <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, November 26, 2004 1:34 PM
Subject: [pure-silver] Re: When is Sulphide toner not 
sulphide toner?


> The question remains:
>
> Can one use thiourea (thiocarbamide) instead of 
> polysulfide for direct
> toning and get the same archival properties? I only 
> considered them for
> indirect toning. The lack of odor would be reason enough, 
> the lack of color
> change another benefit for many. Why are we still buying 
> polysulfide toners?
>
>
>
>
>
> Regards
>
>
>
> Ralph W. Lambrecht
>
   In a bleach and redevelop toner Thiocarbamide converts 
the rehalogenated silver into silver sulfide just as sodium 
sulfide does. It is as archival.
   Indirect toners can not be used for partial toning 
because they don't tone all the silver. While this can be 
used to produce some interesting split toning effects it 
does not result in full protection of the silver image. 
Polysulfide toners, when the stock solution is stong enough, 
can be used for partial toning and tone all densities 
evenly. Some minimum part of the silver must be toned to 
result in full protection but any toning will result in some 
protection. The minimum probably varies with the material. 
According to IPI it is 60% for microfilm. The degree of 
toning is found by bleaching out the silver image with a 
dichromate bleach and measuring the density of the remaining 
image.
   Note that Polysulfide toners work on silver images 
directly and do not need a bleach step Thiocarbamide works 
as a "redeveloper" where the image has first been bleached.
   Polysulfide toners can be made to have low odor by 
keeping the pH fairly low. The IPI toner contains Borax 
rather than carbonate as does KBT. I have never seen a MSDS 
for Viradon. The only ingredient shown on the label is liver 
of sulfur. Liver of sulfur dissolved in water will work 
without an added alkali.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 

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