Finally I have a real question. Given what you have said, what would the difference in the pH be of (say) your P-C-Borax developer above using an unlikely but possible scenario that one had a box of pentahydrate versus a box of pure decahydrate and made the developer from one or the other?
Approximately 20g /litre would show a difference of how much pH?
My suspicion is that the single decimal place pH meter wouldn't help one distinguish the one from the other. Yes/no?
We like to catalog and categorize things to make general rules about how to change things. We have solvent developers, non-solvent developers, high acutance developers, and on and on. With a good lens sharply focussed on the subject of interest, why should we not be satisfied with what we saw on the ground glass or in the viewfinder? How would you categorize a sulfiteless solution of Phenidone, ascorbic acid and borax in water? I did it to see what would happen. Where's the preservative? How can I have fine grain without a silver halide solvent? Thus far, I have tested only HP5+ and Arista EDU 400, and I have 11x14 prints that show no grain from greater than 6" viewing distance.
Of course, ascorbic acid is an antioxidant. At the pH of borax, one could wait all day and not see any sign of development, but add a pinch of Phenidone and Voila! Is it synergism, or simply rapid regeneration of Phenidone by the ascorbate, or are both the same? Is the ascorbate also a solvent of silver halides? I have read that it is a surface developer which fact makes its grain finer, but it wasn't even a developer until I added the Phenidone. But who cares about all this if it works?
Forgive the ramble.
I was all set to process my 2kg of borax as you describe (except I was planning to return the supernatant to the boiler each time for the next 500g so's not to lose the 47g/l) when I went to Google and found the MSDS for both brands that I have here. They are both described as tetrahydrate 99/100% depending on the brand.
I put away the kettle and borax.
My final move would've been to cool the last supernatant in the photo fridge to get almost all the borax back.
Selling tetrahydrate makes sense commercially - why give the customer the more concentrated pentahydrate if one can sell some water with it?:)
The P-C-Borax does indeed work well. I especially liked it with Copex rapid as a stand developer. I just don't know how long it lasts, made up. I used it as a one-shot. Borax is much more soluble in glycerine and ethylene glycol - maybe it's possible to make a concentrate?
The problem is not always in what you bought, but in how long and under what humidity conditions it has been kept. When you open the container, if the humidity is low, some of the decahydrate is likely to become pentahydrate. Over the course of time, although the borax can still be considered to be the same purity as when you got it, the water content may not be. Or, it may be. If it's in a saturated solution, you know the equivalent weight % of the decahydrate by the temperature of the solution, but there's a lag. But if you make a saturated solution at a given temperature, let it stabilize, and decant some of the liquid, that part will have that same concentration at any higher temperature. It's really a simple thing to do and is common lab practice where accuracy is important. If your borax is pure enough, there is no need to do the purification steps, but it's still a good idea to keep the saturated solution. It is much simpler to measure out a certain liquid volume to the nearest ml than to weigh out to the nearest 0.1 g. Besides, if you really think 0.1 gram precision is required, you may not get it with a solid that has two possible states of hydration.
Not only was I going to ensure there was tetrahydrate (not necessarily for long, you tell me) but since the stuff is so pure it was my intention to allow any small amt. of impurity build up in the supernatant as a solution without tossing 47g/l every time. Just being frugal.
My daughter noticed the temperature gauge shoot up and sped home in case it blew up!
Murray, I'm not upset with you for tinkering with my illustrations. I'm posting the comparison that really counts, the one between SPF-3 and Rodinal 1+25. All I have to do now is find where I saved them.
They are "hybrid" photos, using a flat bed scanner at 600 dpi to read 11x14 analog prints. If you print them to 8x10, you should view them from about 6 ft to get proper perspective.