Re: clearing dichromate stain

[Katharine Thayer <kthayer@pacifier.com>]

Charles, in my gum universe, the "usual recommendation" for clearing  
dichromate stain is 5% sodium bisulfite, not bisulfate, or 5%  
potassium metabisulfite is also commonly recommended.  I've used both  
and don't see any reason to prefer one over the other.

However, I had a vague recollection I'd tried sodium sulfite once,  
but didn't remember how it had turned out. Thanks to alt-photo  
archives I can tell you that in side by side tests,  5% sodium  
sulfite worked as well as 5% potassium metabisulfite but took longer  
to clear (the metabisulfite took 5 minutes and the sulfite about an  
hour). It left a faint grey stain behind, but I was using unpigmented  
gum so I could really see the effect; probably with pigmented gum you  
wouldn't be able to see that slight residual.

Katharine


On Dec 11, 2006, at 11:54 AM, ryberg wrote:

> Folks,
>    The usual recommendation for clearing dichromate stain is a 3%  
> or so solution of sodium bisulfate.  In her "Condensed Alt  
> Processes" book Christina says "some use 5% sodium sulfite" but  
> that didn't work for me.  Do I remember correctly that sodium  
> sulfite plus sulfuric acid makes sodium bisulfate?  (My last chem  
> class was 50 years ago.)
>    Also, I have a very dim recollection that a weak hydrochloric  
> acid bath is supposed to work--or have my gray cells misfired?
>    Bisulfite is a mail order whereas sodium sulfite and  
> hydrochloric acid are available within a couple of blocks.
>    There is no sunshine and won't be for many months here in  
> Portland OR.
> Thanks for any help.
> Charles