So, in a single run emulsion, pAg will start low in the kettle and increase as the excess of halide is exhausted, and also rise slightly because of the slight solubility of the AgBr.
In a double run, then, you can regulate the excess of halide and therefore control pAg, or at least keep it somewhat constant. (barring the sensor)
Then that's why you pretty much have to use a double run with specific concentrations of salt and silver to get a specific grain?
At the start of a run, say with 0.1 m/l of NaBr at 40 deg C, the pAg will be about 10.5, the vAg will be about -50 mv, and the pBr will be about 1.1 So, in a single run, the pAg is high at the start, not low. It decreases as you add silver, so that if you add 0.05 m of silver to this kettle, the pAg will drop to about 10.2, the pBr will rise to about 1.4 and the vAg will be about -34 mv.
So, you have it pretty much backwards in your first paragraph.
A double run has two effects. It makes the size of the crystal more uniform, and it controls the type of crystal formed. A chart of the latter was posted here in another thread.
Had one of those light bulb moments... THanks.
IDK if anyone has asked but what form of gold should be used? I've seen HAuCl4 and a K2AuClsomething, plus a seller on ebay selling liquis gold chloride labeled AuCl3.
Jim Browning has the exact amount and name on his web site. Do NOT try to use this on the Azo type emulsion.