Pyrocat HD formula

[luxikon]

I found two different types of formulas for Pyrocat HD. One says Sodium Bisulfite the other Sodium Metabisulfite. Is there any difference? Which one is right?

 

[Ian Grant]

There's a whole thread about Bisulphite/metabisulphite. In the US they are sold as one and the same, although there is a difference. In Europe Metabisulphite is cheap & common, true Bisulphite is expensive as it's unstable. US Bisulphite is usually a mixture of Bisulphite & Metabisulphite.

So Metabisulphite is fine.

Ian

 

[luxikon]

Could not find the thread, Ian. But I don't care because your information pleases me.

 

[Marczak]

There's a whole thread about Bisulphite/metabisulphite. In the US they are sold as one and the same, although there is a difference. In Europe Metabisulphite is cheap & common, true Bisulphite is expensive as it's unstable. US Bisulphite is usually a mixture of Bisulphite & Metabisulphite.

So Metabisulphite is fine.

Ian

Wow.

Thank you

I was so confused with that. I want to start with pyro for my 18x24 cm camera, but make it more whole plate like

`In Europe Metabisulphite is cheap & common`

That`s true!!!!

I can`t find Sodium Bisulfite in Poland, but metabisulphite is common and really cheap 5$ - 500g.

Thank you once again.

Paul

 

[Adrian Twiss]

I make Pyrocat HD up with Sodium Metabisulphite with no problems at all.

 

[gainer]

I mix Pyrocat HD stock A in propylene glycol. A small amount of ascorbic acid takes the place of sulfite or bisulfite for catalyzing the Phenidone-catechol interaction. The B part is the same for all the Pyrocat series.

 

[sanking]

Pat is correct. The purpose of the bisulfite or metabisulfite is two fold, to preserve the stock solution, and to release a small amount of sulfite into the working solution when mixed with water.

When mixed in glycol there is no need for a preservative, and the ascorbic acid plays the same role as sulfite in the phenidoen/catechol interaction, and it also has some advantage in slowing down oxidation. I will probably at some time in the future ask the folks at Formulary to start mixing the glycol version of Pyrocat-HD with ascorbic. But then there would be another question to ask about different formulas!!

Sandy King

I mix Pyrocat HD stock A in propylene glycol. A small amount of ascorbic acid takes the place of sulfite or bisulfite for catalyzing the Phenidone-catechol interaction. The B part is the same for all the Pyrocat series.

 

[Marczak]

Thanks.

Paul