Back To E12/XX for a brief update.
I ran a test at 6 min. with the XX and had noticed a different shape to the curve. Today I printed the patches and was surprised to see what resulted, until I remembered that curve. There seems to be a slight reduction in the densities of the lowest zones (diminished speed), then the straight line portion parallels the 7.5 minute with the Same Slope and the shoulder droops considerably! Visual inspection of the zone patches printed gives the same information. The values of zones 5 and 6 are diminished but not quite out of their ranges, and from 7 on up through 10 there is a subtle gradation finally reaching pure white at zone 11. Holy Cow!
I find this very interesting, and it obviously demands a retest to verify. The implications of this, if it is really true, suggest that in some circumstances, notably nighttime, E12 could actually be quite useful in contraction, because although there is a slight loss in speed, the persistence of contrast in the lower to mid values is something that really gets missed when short timing night/performance images. The drop in the shoulder would prevent those awful burned out whites. Of course, this requires the opposite of the normal mindset; "pull" instead of the usual "push". That's what I do anyway; I turn to staining surface development. This seems to add another tool.
I've found it to be true in the past that the apparent limitations of a technique often prove advantageous in strange and surprising ways. This seems somewhat similar to printing Windisch pyrocat negatives (heavy yellow-brown stain increasing proportionally to the silver density) using VC filters; the proportional stain produces progressively lower contrast in the highlights since it acts as a progressive soft filter. This makes it possible to get great separation in the shadows/midtones with sometimes difficulty getting the whites to be really white even in light sources! Useful, but not for everything.
I processed a roll I shot under overcast light over the weekend, processed at 7.5 minutes. These are extraordinarily beautiful negatives. Very clear, appear a bit thinner than I am accustomed to when all is well, but I know they're going to print not just "jes' fine" but a great deal better. Breathtaking negatives, actually. Through a glass, fantastic.
By the way, I've settled on a working ISO of this film/dev combo of 160, with a normal time tentatively set at 7.5 minutes. The numbers check out great, with zone 6 at about .97, but how's it going to look in real images? Anyway, I'm so close, I have no doubts about using it now.
One of these days, I'll actually have some pics. All this testing. I'm glad I enjoy it.