That makes more sense.
That makes more sense.
The concentrate works! Here are the two curves of XTOL versus concentrate:
As you can see, they're about the same as mixing ingredients separately, and the dev closely follows XTOL. Grain is the same. So dissolving everything into propylene glycol didn't hurt anything, despite a little scare I had when the liquid turned orange and clear again because I dissolved things in a different order. I suggest following the order below:
Propylene glycol .................... 25 ml
Sodium metaborate 4 mol ..... 6.7 g (dissolves in about 3 minutes)
Ascorbic acid ......................... 8.5 g (dissolves in 7-10 minutes)
DimezoneS/Phenidone .......... 0.2 / 0.105 g (dissolves instantly if ground in mortar-and-pestle)
Propylene glycol to ................ 33.3 ml (final volume)
Heat to 90C to dissolve everything and drive the water out of the metaborate.
To make one litre of developer, mix 33.3 ml of concentrate into water containing 90 grams of sodium sulfite. That's 1+29 dilution.
Times are same as XTOL. Target pH is 8.33.
The only change to the formula above was to start with 25 ml of PG instead of 24 because the powders expand the liquid less than I expected, so you can start with a bit more.
Whew! This has been a long project, and I still need to run tests on sharpness and different kinds of film. But this is looking good.
@Alan Johnson: This concentrate is similar to D316, except for adding more metaborate to boost pH. So the keeping-test you're doing will be helpful for this as well.
patent for XTOL lists the final pH as 8.20+/-0.05 which takes into account all the variations in the ingredients and the mixing process they considered at the time. You have done very well to get so close and it may not make any practical difference to the grain, sharpness or the characteristic curve.
As far as I know there is no standard test for developer keeping properties.It seems to depend on the volume of air in the bottle compared to the volume of developer and how often the bottle is opened.
My test has about 20% developer concentrate 80% air and the bottle is opened to air about once a month.
There is an open tray keeping test for developers that we used at EK. I have reported this elsewhere on APUG.
Place 1 L of developer in a standard 8x10 tray. Develop a step wedge in it. Cover with a plastic lid. Keep for 24, 48, etc hours and retest. The change in the curve will show keeping and capacity if done with the proper procedures.
Your curve only seems to go up to 1.5, which is what, 5 stops? Why not take it out to 3.0?
You need a wedge with 0.3 (one stop) density changes for this job. You can get them from Stouffers.
One difficulty is ascorbate is hard to find, so to clone XTOL, one must separately convert some ascorbic acid into ascorbate by adding sodium bicarbonate (baking soda). The problem with that is if the correct amounts of both ingredients are mixed, it will theoretically take a nearly infinite amount of time to convert all the ascorbic acid. To see why, suppose there is one molecule remaining of each ingredient. It will require perhaps years of stirring before those two molecules touch each other. So to complete the conversion in reasonable time, an excess of bicarbonate is needed. But what will that do to the developer?
So I developed one test-strip in XTOL, and a second in XTOL with 0.5 g/L of bicarbonate added. Their characteristic curves are virtually identical, and grain looks the same (but I didn't check sharpness). It appears that a small amount of bicarbonate won't hurt an XTOL-like developer, so it's feasible for home-brewers to create ascorbate this way. But I need to try the dev with and without DTPA to see if that makes any difference. Mytol dropped it, so I doubt it helps image-quality any.
I've years of pH experience measuring everything from Deionized water to hazardous wastes, and pH can be a very tricky test for something that appears to be so simple. Something as simple as stirring can have great affect on some types of samples.
I've come to the conclusion that the whole number in a pH reading is pretty reliable. The first decimal can be accurate, but it is sometimes not very precise depending on the sample. The second digit has much less accuracy than the first, but it can be measured well if your setup is good and you have experience making those types of readings. The third digit in a pH reading, except in some special setups, can pretty much be used as a random number generator.
Don't get all uptight about a difference of 0.03 pH units!