Potassium Oxalate........why so much?

[Jorge]

I have a question that has been bothering me lately. In reading my references for pt/pd printing some people use 450 gr of PO in 1350 ml of water, some use 200 gr in 1000 ml of water, and I am wondering why so much?

I have not calculated the stoichiometry of developing Pt/pd but lets say it is one to one. For example it takes 1 gram of PO to reduce a 1 gram of pt/pd to its metallic state, why use so much then in the developer solutions? Has anybody tried using less? In a pt/pd print depending on the size typically there is from 1 to 4 or 5 grams of pt/pd so I am thinking.....heck if I make a 10% solution I should be good to go.....

I know some are thinking "why dont you try it dummy?"...I will but is always good to ask so that you dont waste valuable solution on something someone might have done before....

 

[avandesande]

I thought that people would re-use the developer bath?
--Aaron

 

[Jorge]

Yes, the developer is reused, but some techniques, specially in high contrast emulsion are better if you include the restraning in the developer instead of the emulsion. So this might require to have 4 or 5 bottles with different concentration of restraining in it. As you can imagine if you are using 1 gal developer per 12x20 sheet then 4 or 5 gallons of PO at 30% can become a very expensive proposition, I am thinking if I can do a 10% solution the this thecnique would be great and not so expensive.

 

[clay]

It may work at reduced saturation, but all the textbooks seem to indicate that it should be at maximum saturation. If I can dig it up, I will email you off-list with some instructions from Carl Weese for making your own K-Ox developer from oxalic acid and potassium carbonate, both of which are dirt cheap on their own. You'll need some way of measuring pH, but other than that, it is fairly straightforward. You mix it by the bucketload this way.

 

[Jorge]

Thanks Clay, that would be great!