As a general rule I recommend a minimum clearing time of about four minutes in a 3% citric acid solution. If your paper is already completely clear after development (and this is a very good thing) it would probably be safe to reduce clearing time in the citric acid from four to two minutes. Or, you could continue to clear for four minutes and reduce the strength of the citric acid solution to 2%. Either procedure will result in less bleaching of the image.
Originally Posted by philsweeney
This is the procedure that I was given by Carl Weese a few years ago:
Put two liters of cold water in a large bucket. Stir in 600 grams of oxalic.
Don't worry about dissolving. Measure an equal amount of potassium hydroxide and very slowly add. The mixture will bubble up lots of CO2 and get real hot when the second ingredient is added. Next, use Ph test paper to
check the solution. You want dead neutral. Add tiny amounts of either acid
or alkalie until it's neutral. This is the only tricky part--amazingly small
amounts shift the solution from acid to base and it will take a while to
find exact neutral.
Let me add a few notes to the description above. This will make a solution that is about 25%. I believe saturation is around 30%, so you may run into issues wit material falling out if you get too close. Just add more water. In most cases, the saturation of PO is not critical for developing, so this should not be an issue.
Definately use COLD water, as the reaction makes a lot of heat. Also, use distilled water to avoid contaminants. For pt/pd, I make the solution pH neutral, and then add a little more oxalic, because the pt/pd chemicals are quite adverse to a basic solution, and I want to make sure that the error is on the side of acidic.
Also note that The Chemistry Store has great prices on citric acid, sodium sulfite, and a handfull of other useful alt chemicals.
Thanks Michael and Sandy. Michael, I have the recipe in my notes now.
I want to also thank Michael for the information about mixing potassium oxalate, and for the link to the Chemistry Store. Sounds like a good resource.
A couple more notes about sodium citrate and potassium oxalate. With kallitype there is virtually no difference between the two developers so far as I have observed. When the image is toned with gold, palladium or platinum both developers give the same tone and image color regardless of developer temperature.
With palladium there is some difference in results because if you use potassium oxalate at a very warm temperature the color of the print becomes much warmer. With sodium citrate the look is almost identical regardless of whether you use the developer warm or at room temperature.
BTW, it is also possible to save money by mixing your own sodium citrate, using sodium carbonate and citric acid. However, since sodium citrate is already fairly inexpensive I have never bothered to make the mix.
There is one other thing about mixing PO that you may want to know. I have mixed up batches a half dozen times in the last year and a half or so, and I noticed that I got a slightly cloudy solution when I changed chemical suppliers a while ago.
It appears that one of the component chemicals is not absolutely pure, and there is a slight brownish look to the solution. PO should look totally clear in solution.
I have used the PO without any problems for pt/pd printing, however the contamination could be an issue in another process. It is too fine to filter with a coffee filter, but a student grade filter will remove it.
I made a handful of filtering cylinders out of old plastic wide mouth bottles, by drilling holes in the lid, and cutting the bottom off the bottle. I screw the filter paper in the lid, invert in a tray and fill with the PO. It slowly dribbles through the paper and the residue that is left behind looks like an iron product.
Anyway, I don't think it is necessary to filter it, but you can if you want to start with clear PO. I suspect that if you started with reagent grade chemicals, there would not be a need for the filtering.
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