The order that ingredients are dissolved into a propylene glycol-based concentrate is important!
I made more concentrate today, and followed my formula in this order (at about 90C):
Order 1: propGlycol=24ml, s.metaborate=6.7g, ascorbicAcid=8.5g, dimezoneS=.2g
The clear liquid turned yellow upon adding the dimezone. Then it became cloudy, with lines of chemical-scale appearing on the bottom and sides of the beaker and growing. After a few more minutes, the bottom was almost entirely covered with scale. The solution ended up being thickly cloudy with what seems to be fine particles. And highly viscous.
This is similar to what happened in Feb 2012 after creating a highly concentrated concentrate. After a few days, some cloudy streaks appeared in it, and it became completely cloudy upon heating, and ended up looking like milk. Also highly viscous. Here's my posting about it from Feb 2012:
My query is the sixth posting.
So I changed the order to this, completely dissolving each before adding the next: (still at about 90C)
Order 2: propGlycol=24ml, dimezoneS=.2g, s.metaborate=6.7g, ascorbicAcid=8.5g
I got the same behavior I mentioned a couple of days ago: The solution turned orange upon adding metaborate, and clear again upon adding ascorbic acid, and it fizzed upon adding the ascorbic acid, with visible foam.
With the clear-to-orange, and orange-to-clear, and fizzing, it's obvious that reactions are occurring in the propylene glycol solution in Order 2. Also, the yellowing and cloudiness and scale and high viscosity are different reactions occurring in Order 1.
Do the chemists here have any idea why dissolving the DimezoneS first versus last makes such a large difference?
PS @Kirk: Okay, I won't bother if a pH-difference is small. One trick I use is to quickly go back and forth between my test-developer and XTOL (known to be 8.29). Think of it as a minute-by-minute calibration. I've been able to get repeatability within +/- 0.02 doing this. But getting that initial measurement of XTOL requires a real calibration, which one hopes will stay true for half an hour.