Potassium Metabisulphite

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vickersdc

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Hi,

I'm just about to embark on producing my own glass plates, using a gelatin subbing layer and simple emulsion. However, I also want to try out a pyro developer solution that I found in a c1900 book called "Everyones Guide To Photography".

The recipe calls for 1oz pyrogallol and 1oz potassium metabisulphite.

Can I just confirm that this is the same stuff as used for wine-making, and that all I need to do is visit my local home-brew shop?

Thank you,
David.
 

dancqu

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Your local home-brew may have the same
chemical if by the same name. Take a close
look at the label.

Potassium bisulfite is an equivalent save for
the amount needed to exactly equal the
metabisulfite amount. Dan
 
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vickersdc

vickersdc

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Thanks Dan.

I just had a look at some Campden Tablets that we use for wine-making, but they are Sodium Metabisulphite, rather than Potassium Meta.

How does one convert amounts required between bisulphite and metabisulphate?

Cheers,
David.
 

Ian Grant

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Potassium Bisulphite isn't strictly a direct equivalent it's less acidic so slightly more needs tro be used. You can substitute 84 parts Sodium Metabisuphite for 100 parts Potassium Metabisulphite.

The Bisulphite forms tend to be US and are a mixture of Bisuphite & Metabisulphite, in Europe it's all higher grade Metabisulphite sold as powder.

Ian
 
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vickersdc

vickersdc

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Thanks Ian,

That means that instead of 1 UK ounce (or 28.4 grams) of Potassium metabisulphite, I can use 23.8 grams of Sodium metabisulphite. I'll crush a couple of those Campden tablets up and see how we go.

Is there anything else that I should be aware of when substituting Sodium meta. in for Potassium meta. (in my pyrogallol developer)?

Thanks everyone for your help.
David.
 

cp16

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A large container of potassium metabisulphite is dirt cheap from silverprint anyway
 

cp16

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sorry my mistake it's sodium metabisulphite ive bought from silverprint (just double checked the label on the jar whoops) it's probabily worth giving them a ring to check anyway but if you want to substitute with sodium metabisulphite i think it was only around £3.50 for a 500g container last time i bought any.
 

paul_c5x4

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I'm in need of a bunch of chemicals myself, potassium metabisulpite being one of them. Found a source that can supply 250g packs - way more than I need.

vickersdc - Drop me a note, and I'll send you some when it arrives.
 

paul_c5x4

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Just came across a Dead Link Removed (possibly quoting the original source that Ian mentioned).:

Crabtree and Mathews (1938) stated as follows: "Ordinary sodium bisulphite has been shown by analysis to consist chiefly of metabisulphite which is converted into bisulphite when dissolved in water. Sodium bisulphite may be substituted weight for weight for potasssium metabisulphite."
 

Mike Wilde

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Sorry I'm so far away - I was just recently gifted with about 1kg of K metabisulfite. The only down side is that there were about 300 bits and bob of chem bottles to sort though to find the relevant photographic and non photographic chems of value to me.
 

Ian Grant

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Just came across a reference (possibly quoting the original source that Ian mentioned).:

Crabtree and Mathews (1938) stated as follows: "Ordinary sodium bisulphite has been shown by analysis to consist chiefly of metabisulphite which is converted into bisulphite when dissolved in water. Sodium bisulphite may be substituted weight for weight for potasssium metabisulphite."

Except for one problem, the writer hasn't read the full conclusions, there's a later paper, Kodak researchers found that they weren't quite interchangeable in equal proportions in all circumstances.

I don't have the reference here in Turkey but there is a small percentage difference, and the Grade of Metabisulphite produced in Europe is higher than the US products sold as Bisulphite. This can have a bigger impact where a developer or fixer uses larger quantities as a preservative or to control pH.

In general though with a Kodak formula which includes Bisulphite then Metabisulphite is fine, but when a formulae stipulates Metabisulphite then it's better not to use Bisulphite.

The first Crabtree paper compares Potassium Metabisulphite with Sodium Bisulphite, but not Sodium Metabisulphite which is another issue and was investigated by Kodak Research at Harrow (UK).

Ian
 
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paul_c5x4

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Thanks for that Ian - I've just mixed a batch of D85 which called for 11g of Sodium Bisulphite which I substituted with 11g of Potassium Metabisulphite. Hopefully for my needs, the two are interchangeable - Will see when I do my first lith print with this mix :smile:
 

rx7speed

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sorry to jump in but I am hoping it is at least acceptable as it is related to the topic at hand but what is the potassium metabisulphite used for in the developer?
 

Ian Grant

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Potassium Metasbisulphite or Sodium Metabisulphite - is used for more concentrated solutions when its acidic nature gives a far greater preservative effect than Sulphite. To counter this more alkali accelerator is added in some developers. It is often used in Amidol, Pyrocatechin and Pyrogallol developers.

It is also be used in pre-packed powder developers as a preservative, Microdol-X (powder) and Bromophen are two example it's, but it has been used to lower the pH in Ultra Fine Grain developers.

Ian
 
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