[pure-silver] Re: RC to FB

----- Original Message ----- 
From: "DarkroomMagic" <info@xxxxxxxxxxxxxxxx>
To: "PureSilverNew" <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, December 31, 2004 5:28 AM
Subject: [pure-silver] Re: RC to FB


> Toning is more critical with FB paper, because RC is more 
> forgiving to
> processing errors. According to Ilford Technical Services, 
> sulphide toner
> also reacts with residual silver, compensating to, some 
> degree, this
> processing error. Residual silver (or fixer) in RC is rare 
> compared to FB.
> That's why there is less need for sulphide toning.
>
> However, it is still recommended for both, and I do agree 
> that the toning
> issue is the same for RC and FB, if both have been 
> processed 'properly'.
> Unfortunately, 'properly' means different things to 
> different people.
>

    Ilford's remark is curious. Sulfide certainly does react 
with unfixed halide and with fixer reaction products: it 
tones them. This can result in veiling of highlights if the 
print is not fixed fully. A weak solution of sodium sulfide 
is a standard test for completeness of fixing because it 
leaves a stain if there is an residual halide.
    I don't see how this compensates for incomplete fixing 
or washing, it simply produces the effects of age right 
away.

> BTW, I thought of one more difference between RC and FB.
>
> The issue of 'mirroring' seems to be more of a problem 
> with RC, due to the
> plastic layer below the emulsion, making a silver 
> stabilizer like Sistan a
> worthwhile last processing step. I still do it for RC and 
> FB paper, despite
> the fact that I use 2-step film-strength fixing and 
> selenium/sulphide toning
> for FB. Some consider this over-the-top, but I don't see 
> how it can hurt.
>
>
>
>
>
> Regards
>
>
>
> Ralph W. Lambrecht
>
>
   The mirroring is due to migration of silver to the 
surface of the print. It is usually explained as a redox 
process where fine silver is converted to silver oxide by 
atmospheric polutants. The oxides migrate to the surface 
where they can be reduced to fine silver or converted to 
silver sulfides by other polutants. The surface silver can 
be removed but the reduction of the image density can not be 
recovered.
   RC papers of the past suffered from the effects of 
peroxides emmitted by the Titanium dioxide reflective layer 
under the emulsion. This also had the effect of damaging the 
plastic itself, resulting in crazing or flaking. For at 
least ten years RC papers have contained substances which 
prevent this effect. The substances are supposed to be 
regenerating so they don't "wear out" in time. RC should be 
as long lived as fiber. The use of a toner or stabilizer 
will give further protection to RC prints. however, toners 
or stabilzers do not protect the plastic.
   The use of film strength rapid fixer is probably not good 
practice for RC because it fixes out so fast and acid rapid 
fixer can have some bleaching effects. Paper strength 
lengthens the fixing time to about 2 minutes. Rapid fixer 
probably has an andvantage for modern VC papers since their 
emulsions reportedly have some Silver Iodide in them. 
Ammonium fixer is much less affected by soluble Iodide than 
is sodium fixer.
   Neutral rapid fixer, like Agfa Universal Fixer, does not 
have the bleaching property of acid rapid fixers.
   I think toning is especially important for any print 
which is to be displayed. Display prints are subjected to 
much more air polution and more light than stored prints. 
Stabilizers, like Agfa Sistan, are helpful, but I still have 
not seen any reports on accelerated aging tests with it.

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

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