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

Christopher, elemental silver will react with sulfide sources 
without previous chemical treatment, at least to a small extent. 
(This is why silver tarnishes in air -- it reacts with the very 
small amounts of H2S present in air IIRC). It is conceivable that 
you are forming a very thin protective layer of silver sulfide on 
the grains of silver in your paper and that this slows down the 
ferri bleaching process without affecting the colour.

Just a guess...

Jordan


Christopher Woodhouse wrote:
> Thanks Richard, I thought I had read somewhere that Thiourea or
> Thiocarbamide toners do indeed produce silver sulphide. Funny thing is, if I
> dunk a print into the toner, after full fix and wash, it resists a ferri
> bleach more or less the same as a 5 minute 1+10 selenium treatment.
> 
> Some users, who go for the sepia toning for effect, use this pre-tone as a
> way of protecting highlights from any reduction in the bleach and
> redevelopment process.
> 
> What I can't quite understand is, if a print is fully fixed and wash, what
> is the toner working on in this first toning step?
> 
> Chris
> 
> On 27/11/04 5:33 am, "Richard Knoppow" <dickburk@xxxxxxxxxxxxx> wrote:
> 
> 
>>----- 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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> 
> 
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