Pyrocat-HD: Sodium Bisulfite or Sodium Metabisulfite?

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Shinnya

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Hi everyone:

I am trying to mix Pyrocat-HD. There is one thing which is not clear to me after reading dozens of posts from different sources. Nothing seems to confirm or deny it...

Do I need Sodium Bisulfite, or Sodium Metabisulfite is sufficient?

I have read an article in unblinkingeye <http://unblinkingeye.com/Articles/Pyrocat/pyrocat.html> as well as a link <http://silvergrain.org/Photo-Tech/chemistry-misnomers.html> from there which discusses the nature of two chemicals in detail. According to it, there is no practical difference in photographic use EXCEPT "in some sensitive developers, this may make sizable difference in pH."

So my next logical question is:

Is Pyrocat-HD a sensitive developer which pH is very critical?

If anyone with experience in this process is kind enough to confirm or deny it definitely, I would be very happy. Thank you in advance.

Warmly,
tsuyoshi
 

skahde

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My supplier claims that Sodiummetabisulfite, Sodiumdisulfite, Sodiumpyrosulfite are synonymous for the same subtsance. I take from the article by Suzuki that what my supplier sells may be a mixture of (unstable) bisulfite and metbisulfite.

I bought "Sodiumdisulfite" (from a third party), use it for Pyrocat-HD and it seems to work fine. As the difference may be only a very slight shift of pH this can be easily compensated for with development-time without notice as long as certain borders aren't crossed. My estimation is that you are far from that with pyrocat-HD.

best

Stefan
 

sanking

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Shinnya said:
I am trying to mix Pyrocat-HD. There is one thing which is not clear to me after reading dozens of posts from different sources. Nothing seems to confirm or deny it...
tsuyoshi

I have been using sodium bisulfite for years in mixing Pyrocat-HD when this issue came up last November on the alt-photo-process list. After reading the information at http://silvergrain.org/Photo-Tech/chemistry-misnomers.html I decided to compare sodium bisulfite and sodium metabisulfite in the Pyrocat-HD formula. I also compared potassium metabisulfite. I could see no difference at all in the results using any of the three chemicals, and I tested very carefully, down to reading step-tablet densities with a densitometer.

However, as best I can understand the issue, sodium metabisulfite is really what should be used in the formula. It turns out that sodium bisulfite works just as well because most of what is sold as sodium bisulfite consists largely of sodium metabisulfite.

In any event to be on the very safe side of safe my recommendation at this time is to use sodium metabisulfite (or potassium metabisulfite) and I plan to make that change in the formula soon. But if you have sodium bisulfite on hand and want to use it I think the chances are about 99.9% that it will work fine for you.

Sandy King
 

sanking

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Just for the record, this discussion also applies to other Pyro developers that specify sodium bisulfite as a preservative, including PMK.

My presumption is that it would be better to specify sodium metabisulfite in all of these formulas but I would not take the liberty to state this as a fact without testing the premise. Perhaps Gordon Hutchings has said something about this in the past?

Sandy King
 
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