Vaughn you are correct. Heating the developer releases water vapor resulting in an increased concentration. The crystals indicate the solution is beyond saturation at room temp. You can either add water (distilled or deionized) until they dissolve or simply filter them out then add fresh developer which is what I usually do. The actual concetration of the developer is not that critical. It is a good idea to filter out the black grit fairly regularly because it can sometimes stain the paper.
You should also monitor the pH of your PO with litmus paper (a pH meter is more accuracy than you need, and they break too easily). I like to keep my PO around pH 6 by adding small amounts of oxalic acid. Once the developer becomes alkaline (pH 7 or more) it can have a detrimental effect on the print quality. You can also do as Dennis suggests and sprinkle in some oxalic acid once in a while and not worry about the litmus paper.
It ain't rocket science, so don't worry about being too anal about this stuff. Some basic maintenance will keep your developer going for a long, long time.
Jarvman it's easy to make your own PO from potassium carbonate and oxalic acid if you can get those chemicals locally.
Originally Posted by Jarvman
(You may want to do this outside or at least with good ventilation as the process gives off CO2, some heat and a significant amount of bubbles. Think gradeschool volcano project.)
To make 2 Liters:
1. Start with about 1100 ml cold distilled water in a container big enough to handle all the effervesence - maybe a gallon or two.
2. Add 450 grams of Potassium Carbonate mono with stirring until dissolved.
3. SLOWLY add 400 gm of oxalic acid to the potassium carbonate solution with stirring, waiting each time you add the acid until the bubbling subsides. Continue until all of the oxalic acid has been added.
4. Add water to bring total volume to 2 liters. Check the pH at this point. It should be near 7.0 (neutral). Now add more oxalic acid in small amounts and keep checking the pH. When you get the pH to about 6.0, you’re done.
Is the advantage to this in the cost? Or just easier than having it shipped?
Originally Posted by Kerik
If you buy the chems in reasonable quantity it's much cheaper this way.
It's £6.99 for 100g of oxalic acid from retro so its going to work out more expensive this way. there's a chemical company called sigma aldrich that sell everything but you need a business account with them apparently. I never got the chance to try a gradeschool volcano project :(
Jarvman, check with one of the woodcare type shops. Some carry oxalic acid to bleach/clean wood products. Here is a link to a place I found using google and it is 8.75 inc VAT for 1Kg.
Yeah, you need to find a chemical supplier that will sell in much larger quantities. There are many here in the states like The Chemistry Store:
I buy the chems from a local place that sells pool chemicals and the like to the public.
ooh ooh, another thing, how many of you actually presoak your paper before coating it? Leaving it to dry out before applying the pt/pd obviously.
It depends on the paper. I don't presoak unless the paper is too alkaline, in which case it gets an acid pre-soak.
FWIW, I use a large - 2 QT. Pyrex measuring cup with plastic lid to heat my PO. The lid minimizes evaporation and the vapor condenses on the inside of the lid.
Originally Posted by Kerik
As Kerik said filter the sludge and check the pH. Top off with fresh PO as the volume declines or add a little water to dissolve crystals at the bottom.
You are good to go.