After running more tests, I've come up with the following modification to D316 which gives a tighter toe with Delta-400. The 1-litre formula:
Propylene glycol ....................... 10 g (yes, measured in grams)
Sodium metaborate 4 mol ........ 1.5 g
Ascorbic acid ............................ 3.5 g
Phenidone ................................ 0.05 g
Use 14.7 g/L of concentrate with 50 g/L of sodium sulfite. pH = 8.18.
I'm calling this formula "Trial-130119", as that's the date of the first mixing (yesterday). This is also more concentrated than D316. It is very close to something I mixed 4 months ago, so it should not crystallize, but we'll know for sure in a couple of weeks. Note that I raised the sulfite from 45 to 50 g. That was solely to raise pH, but I might drop it back to 45 g. The time for Delta-400 is the same as D316 (17 min), and we'll see how times for other films are affected.
Grain is still a bit finer than Xtol, despite Xtol having the advantage of lower contrast. The scanner was manually focussed on the middle wedge and contrast adjusted to be equal:
Xtol: Attachment 62937 Trial-130119: Attachment 62938
And the curves. Note that the toe is identical to Xtol:
As with D316, highlights are stronger than Xtol.
Fog is higher than Xtol. I noticed D316 produced a bit higher fog with a few films. Trial-130119 behaves the same. My experiments indicate that the fog is likely due to sodium metaborate mixed into propylene glycol, which Gerald Koch said produces esters. Could those esters boost fog? With both D316 and Trial-130119, Delta-400 has 0.12 more fog than Xtol, which is a lot. Fortunately, the scans show that grain is not affected. Maybe add a restrainer anyway?
So why am I fooling with this after burning over 50 rolls testing D316? Because I'm a perfectionist! Those tests showed that D316 had slightly softer toes with a few films, but Delta-400 already has a somewhat soft toe, and I am loath to make it any softer. Delta-400 is an important film, so I want my dev to work well with it.
Your discrepancy just tells me that either your syringe or the MSDS statement of specific gravity probably isn't all that accurate. Maybe even your scale. Without some way to crosscheck your gear, it's hard to know exactly which part is off.
Even so, your ~3% discrepancy is probably not too big a deal. (It would be nice to know the significance, though.)
A question for the chemists here:
Why do I *not* get precipitation when freezing these PG-based concentrates? I put Trial-130119 in the freezer overnight, and like D316, there is no cloudiness nor precipitate. Based on lack of precipitation, I recommend that these be frozen. But I'm wondering: why no precipitate?
Trial-130119 takes longer to dissolve the ascorbic acid at 75C due to its higher concentration and lower proportion of metaborate. So I'm closer to the solubility limit. Yet no precipitation when frozen. Odd.
@Mr Bill - Thanks for the note. You're right, and I hadn't thought of that: I still measure the water by volume because it's impractical to weigh such a large volume and a beaker is accurate enough.
Finally, the curve for Trial-130119 with 45 g/L of sulfite (reduced from 50 g/L in my prior posting) has this curious trait: The toe matches Xtol, and the highlights match D316. Here are all three curves for Delta 400:
The toes are the means of two frames, and my goal of all this was to remove the softness in the toe of the green curve (D316).
Some surprising (and good) results:
1. The Trial-130119 developer (described 3 postings back) will also accept Dimezone S without crystallizing. At least it's now been a week with no evidence of crystallization, and I'll truly believe it when it's gone one month. D316 quickly crystallizes with Dimezone S. I used 0.1 g of Dimezone S in place of 0.05 g of Phenidone. Based on resulting dev-times, I should have used 0.096 g of Dimezone S to keep dev-times the same as Phenidone. With 0.1 g, dev-times must be reduced by 4%.
2. The Dimezone S version produces finer grain and lower fog. I only tested Delta 400 because I've found it's unusually sensitive to developer composition. Here are scans of strips developed in XTOL, D316, Trial-130119/Phenidone and Trial-130119/Dimezone. The contrast of these scans was boosted digitally to exaggerate differences in grain:
XTOL:Attachment 63525 D316:Attachment 63526 T119/Phen:Attachment 63527 T119/Dime:Attachment 63528
To me, the T119/Dime is noticeably better than the others. Clue: Once you've viewed the images, you can quickly switch between them, and the instant image-changes make grain-comparison easy.
The curves of this brew versus XTOL show a good match with the usual higher shoulder:
I was surprised that it did not crystallize with Dimezone S. I suspect the lower metaborate/ascorbic ratio is the reason. It obviously is not related to concentration-ratio because Trial-130119 is more concentrated than D316.
Fog was another surprise. Simply switching from Phenidone to Dimezone S dropped fog by 0.1 log-units (1/3 stop). That's a lot. Delta 400 has higher fog than most films, and metaborate/glycol/Phenidone worsen it. But merely switching to Dimezone S dropped the fog down to XTOL's level (0.38). I like Dimezone S. PE says it stores better, and I find it also gives better image-quality.
I think my next step will be to mix new concentrate using 0.096 g of Dimezone S and verify that image-quality is unchanged with the longer dev-times.
After reading the above posting, I realized it's hard to compare Trial-130119/Dimezone with XTOL because they're separated by two images. Here they are together, so you can switch back and forth between them with one click:
XTOL:Attachment 63530 T119/Dime:Attachment 63531
Some more ideas I have are to (1) eliminate the crystallization issue by replacing metaborate with TEA, because I doubt there will be much difference between 85% and 99% TEA, (2) replace some of the poorly-soluble ascorbic acid with better-soluble hydroquinone to maintain a high concentration-ratio, and (3) adjust pH downward with citric acid. Too many ideas to try and too little time...
Be careful Mark, 85% TEA is usually 15% DEA making the mixture more alkaline than 99% TEA. This will throw off the pH of the developer.
But if the results are good, then why worry as long as you disclose the full details to the readers. Right?
I've tested Trial-130119 with both Tri-X and Delta-400 using Dimezone S. Compared with XTOL, this Trial dev gives the same or a hint worse grain with Tri-X, and noticeably finer grain with Delta-400. Ilford is committed to this market, so I'm making certain that whatever I come up with works well with their films.