[pure-silver] Re: AW: Re: toxicity
- From: <C.Breukel@xxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 19 May 2009 13:12:03 +0200
> -----Original Message-----
> From: pure-silver-bounce@xxxxxxxxxxxxx [mailto:pure-silver-
> bounce@xxxxxxxxxxxxx] On Behalf Of Richard Knoppow
> Sent: maandag 18 mei 2009 16:51
> To: pure-silver@xxxxxxxxxxxxx
> Subject: [pure-silver] Re: AW: Re: toxicity
>
>
> A problem with wet plate is that the silver halide is
> mostly silver iodide which is resistant to fixing. Ammonium
> thiosulfate is a better fixer for it than sodium thiosulfate
> but KCN is the most effective of all. A problem with KCN is
> that it tends to bleach out metallic silver as well.
> Thiosulfates take longer than KCN but are essentially
> non-toxic while KCN is very hazardous.
> KCN was also often used as the fixer when an iodine
> bleach was used but thiocarbamide or ammonium thiosufate
> works as well if given a bit more time. Iodide reducer or
> bleach does not leave yellow stains as ferricyande often
> does (but not if its fixed adequately).
>
> --
> Richard Knoppow
..Hi Richard, it's true that the very first WPC negatives were Silver
Iodide only, but that get a better spectral response and a bit more
speed (think from say 0.12 asa to 0.25asa or so..;-)..) bromide was soon
introduced, so nowadays its silver idonie as well as silver bromide..
Alos tue is that KCN fixes out in 10 sec or so (and can bleach the
image, and if the developper (FerricSulphate) is not washed out enough
you get blue ferri-cyanide, also seen in Daguerrotypie).
Amm.Thiosulphate fixes out in 1-2 min (exhausts quite quick), and
SodiumThio ("Hypo") takes roughly more than 5 minutes..
Best,
Cor
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