Thanks for the postings about sodium metaborate. I was unaware of the history of the "4-mol" and "8-mol" notations; I only knew they are confusing. In the concentrate, I wonder if the degree of hydration makes any difference. That is, I suspect the water is driven out by heat, and if so, the initial hydration makes no difference (except when weighing the powder). It would be easy to experimentally determine if the water is driven out -- maybe I'll do that.
Also, my long posting gives the impression that there's almost no flexibility of quantities of chemicals. That isn't so. If you're willing to decrease the concentration-ratio (i.e., use more PG in relation to the powders), then solubilities are less of an issue, giving you a wider range of feasible quantities.
Today, I ran a test-strip using the D316 concentrate:
pH is 8.08.
13:45 minutes (at 20C) with TMY-2.
Density-curve is very close to XTOL.
Grain and sharpness both match XTOL when compared with my loupes.
The specific gravity of my batch of D316 is 1.146. If you have a scale, measure out 23 grams/L because weighing is more accurate than measuring small volumes with a graduate.
I've found that in D316's formula, you can change the sodium metaborate (4 mol) from 2.0 g/L up to 2.7 g/L, and all will give you excellent developers (mixed directly into water; no concentrate). I was hoping to hit a pH near XTOL's 8.20, because the dev-times of various films would probably be closer to some constant (about 1.9) multiplied by XTOL's time. D316's pH of 8.08 means that constant may vary more from film to film. That's a minor problem. Anyway, I'll try raising pH by boosting the sodium sulfite some and see how that turns out.