Mocon — XTOL-quality in a long-lasting concentrate

Mark A. Overton, April 6, 2013        Return to main page

[2017-10-29: This article was originally posted here on the Photrio web-site. A bottle of this concentrate (and the similar D316 developer) have been in my freezer for about 4.5 years, and they are still fully active with no yellowing, so Mocon will last over 4.5 years when kept frozen. The original article is below.]
Mocon is a two-part developer consisting of a long-lasting liquid concentrate and sodium sulfite powder used one-shot. It was originally intended to be an XTOL-clone, but it turned out to be not quite that. Mocon generally gives slightly finer grain than XTOL and slightly lower true film-speed. To match XTOL, you can modify Mocon, or try Mocon-X which is also described in this article. Mocon stands for “Mark Overton’s Concentrate”, and its temporary name was 214D. The goal of this project was to create a concentrate that lasts a long time (over a year), and that gives the image-quality of XTOL. This developer is intended for those of us who don’t shoot enough B&W to consume 5 litres of XTOL before it goes off.

Mixing Working Developer

You can mix working developer in two ways: (1) Measure concentrate into your beaker, and add sulfite solution (mixed ahead of time) to the fill-line, or (2) Measure both concentrate and sulfite powder into your beaker, add water to the fill-line, and stir until dissolved. Here’s more detail:

Method 1: Alan Johnson had the following idea which makes using this concentrate as easy as Rodinal. First, make a batch of sulfite solution by mixing 46 g/L sodium sulfite into distilled or DI water. Make enough to last a couple of months given how much shooting you do. You can refrigerate it to ensure longevity. To make working developer:

  1. Using a syringe, measure 15.5 ml/L (18 grams/L) of concentrate into beaker.
  2. Pour in sulfite solution to the fill-line.
It’s that simple. As an example, to develop one roll of 35mm film in a stainless steel tank, you’ll need 220 ml (0.22 L) of developer. Measure 3.4 ml (=15.5*0.22) of concentrate with a syringe, and add sulfite solution to the 220 ml-mark. This works out to 1+64 dilution of concentrate+solution.

Method 2: If you don’t want to keep sulfite solution around, you can mix working developer as follows:

  1. Put a plastic beaker on your scale, and press Tare to zero it.
  2. Pour in 18 g/L of concentrate (same as 15.5 ml/L).
  3. Press Tare to zero the scale.
  4. Pour in 45 g/L of sodium sulfite.
  5. Pour in water to fill-line, and stir until dissolved (about 3.5 min at 20C).
For the one-roll example above, you would weigh out 4 g of concentrate and 9.9 g of sulfite into the beaker, and add water to the 220 ml-mark. You can use tap-water if you develop within 30 minutes; waiting longer risks having dissolved minerals in hard water precipitate onto the film.

The pH is 8.08. An electronic scale with .1 or .01 g resolution only costs US$12-15. That’s the cost of three rolls of film, so there’s no excuse to not have one (or two). Search for “scale .1 g” or “scale .01 g” on

Quiz: Why does sulfite solution contain 46 g/L of sulfite instead of 45 g/L as used in method 2?

Making the Concentrate

Mix the concentrate below at 75C, stirring constantly, adding the next ingredient when the current ingredient is mostly dissolved. I use a glass thermometer as a stirring rod so I can stir and watch temperature concurrently. Hot-time will be 20-25 minutes. I suggest quadrupling the one-litre formula below, and mixing in a 100 ml beaker. The quadrupled concentrate fits nicely in a 60 ml bottle, although I suggest using two 30 ml bottles instead. That way, one bottle remains unopened while you use the other, so it’ll last longer. The formula:
Propylene glycol     12.2 g (same as 11.8 ml)
Sodium metaborate 4 mol    1.8 g
Ascorbic acid     4.2 g
Dimezone S     0.08 g (or .05 g Phenidone, but note issues below)
When stored frozen (preferred) or refrigerated, it should last over a year and probably over two years frozen. At room-temperature, count on six months. If you store it frozen, and forget to take it out of the freezer ahead of dev-time, you can immerse the bottle in a pan of water, which will quickly warm it to room-temperature. I don’t advise opening the bottle when frozen to avoid condensation adding water to the concentrate.


Here are the times at 20C. If you agitate constantly for the first 30 seconds, and once per minute after that, these times will give a Contrast Index (CI) of about 0.58, suitable for printing at grade 2. Agitating Mocon once per minute is the same as agitating XTOL twice per minute, because it results in the same number of agitations, because Mocon takes about twice as long as XTOL. All the films below have been tested with Mocon, measured and graphed, and are known to work fine.
Tri-X     13.5
T-Max 100     14 (see note below about early shoulder)
T-Max 400     13.5
Delta 100     12.25
Delta 400     18 (see note below about long toe with Phenidone)
Delta 3200     25 or longer (not recommended due to some speed-loss and long dev-time)
Pan-F+     12.25
FP4+     16
HP5+     15
Acros     15
Neopan 400     14.25
As mentioned above, Mocon generally gives slightly finer grain and slightly lower film-speed than XTOL. However, this difference varies among films. For example, I could see no difference with Tri-X. The speed-loss is small enough that I’ll accept the finer grain in trade. If you want the same film-speed as XTOL, boost Dimezone S to .1 g/L in the concentrate and reduce dev-time by about 5%. For pushing, I suggest boosting Dimezone S above .1 g/L, but this change needs testing.

Further Notes

T-Max 100 has exceptionally fine grain with Mocon, but has a very early shoulder, forcing you to meter accurately at box-speed (EI 100). This early shoulder also occurs with some other popular developers. You can think of Mocon as a highly compensating developer with T-Max 100, probably even more so than Diafine. It will compress bright highlights for you, but overexposure will reduce gradation in normal highlights. The grain Mocon gives you is considerably finer than XTOL, and sharpening is the same. That finer grain is worth the effort to meter accurately.

If you choose to use Phenidone instead of Dimezone S, you’ll see two changes. First, Delta 400 will get a longer toe, so you should rate it at 200 or slower. Second, Phenidone increases fog by .02-.10 depending on film. Neopan 400, FP4+, Delta 100 and Delta 400 get the greatest fog-boost. T-Max 400, Tri-X and HP5+ get little fog-boost. I recommend Dimezone S which can be purchased in both Europe and the USA with international shipping. Mocon has the following advantages over XTOL:

Mocon has the following DISadvantages compared with XTOL: Based on the formula, you might think Mocon is the same as XTOL diluted 1+1. But Mocon was designed to have twice the dev-time of XTOL with half the sulfite, which you don’t get with 1+1 dilution. PE confirmed that, within limits, doubling time and halving sulfite will have the same solvent-effect.

Alternative Similar Developers

The four components propylene glycol (G), sodium metaborate (M), ascorbic acid (A) and Dimezone-S (D) or Phenidone (P) can be combined in different quantities. Sodium sulfite (S) is added separately for all such developers. Here are some of the better ones I’ve tried:

Mocon-X, which had the temporary names of 119D and 119P, produced results identical to XTOL with the few films tested. Its one-litre formula is:

G=10g, M=1.5g, A=3.5g, D=.1g -or- P=.05g
Usage: 14.7g concentrate and 45g sulfite in 1L of dev (pH=8.15)
Here are the few times that I determined:
Tri-X     13
HP5+     14.25
Delta 400     17.5
Neopan 400     16.25
Notice that these times are slightly lower than those for D316 described below, so the D316 times minus a bit would be good starting points.

If you want to create a developer that’s good for pushing, I suggest boosting the Dimezone S in Mocon-X to .12g or higher. I think the increased concentration of developer will cause increased exhaustion in midtones and highlights, giving the toe more time to develop, increasing true film-speed. But grain will be a little worse.

D316 was first formulated in January 2012, was tested thoroughly, and performs similarly to Mocon, but I rejected it because it produces a longer toe with Delta 400, and also because it can only use Phenidone (not Dimezone S), resulting in higher fog. Its one-litre formula is:

G=16ml(=16.6g), M=2.2g, A=4.5g, P=.05g
Usage: 20ml (=22.8g) concentrate and 45g sulfite in 1L of dev (pH=8.08)
The times for D316 are:
Tri-X     14
T-Max 100     13.75 (shoulder is higher than Mocon, but still lower than most films)
T-Max 400     12
Delta 100     13
Delta 400     17
Delta 3200     25 or longer
Pan-F+     12.25
FP4+     16
HP5+     14
Acros     13.5
Neopan 400     16.5
Locon-1 was another discovery from January 2012, and is suitable for pushing or low contrast. But it has had little testing. Its formula:
G=17.5ml, M=1.2g, A=2.8g, P=.15g
Usage: 20ml concentrate and 35g sulfite in 1L of dev (pH about 8.2)
To reduce fog, I suggest using .2 or .25 g of Dimezone S instead of Phenidone. Starting dev-time is 8-10 minutes for T-Max 400. This formula has relatively little ascorbic acid and sulfite, so restoration-rate will be lower and thus the developer will exhaust more quickly in midtones and highlights, so the toe will develop even more than modified Mocon-X.

SMAP Family

All developers described in this article are members of what I call the “SMAP family”, where the letters S-M-A-P stand for Sulfite, Metaborate, Ascorbic acid and Phenidone. Dimezone S is part of the Phenidone family, so it’s included. You can create a surprising variety of developers using only the four SMAP chemicals. And many of them can be mixed as concentrates. Locon-1 has SMAP = (35, 1.2, 2.8, .15p), where the “p” at the end denotes Phenidone. And “d” denotes Dimezone S. Mocon has SMAP = (45, 1.8, 4.2, .08d/.05p).

The SMAP of (90, 6.7, 8.5, .2d) is a developer with the same dev-times as XTOL, same image-quality and same pH. It appears to be a clone of XTOL in all respects. But the concentrate crystallizes after a week or two, separating into a cream and liquid (more about this problem below), so it’s unusable as a concentrate. However, you can mix the formula directly into water and omit the propylene glycol. If you want to try this, I suggest dissolving the Dimezone S in a separate 2% solution of propylene glycol to make the small quantities easy to measure. Also, propylene glycol changes developer behavior a little, and its absence means you might need to change the 6.7g of metaborate a little to perfectly match XTOL. Rolls of HP5+, Acros and Tri-X all matched XTOL.

PC-Sulfite is what I call the “D-23 of PC developers” because it’s so simple. Its SMAP is (90, 0, 2.8-3.5, .15p). Notice that it has no sodium metaborate. Add about 15% to XTOL’s times. Grain is the same as XTOL or a bit worse, depending on film. Although I haven’t tested it, I suggest using .2g of Dimezone S instead of Phenidone. Using less Phenidone or Dimezone S should improve grain a little. Peter Svensson independently discovered it 5-1/2 years before I did, and his SMAP was (64, 0, 3, .08p). Here’s my posting about it: Here is Peter’s posting:

Here are some more interesting SMAP developers that I haven’t had time to pursue. Each has been tested only once, except Instant Mytol which I’ve never tried. All except Instant Mytol can be mixed as a concentrate:

(75, 1.5, 4.5, .08d/.05p) My notes say “top quality”. Use about 2X XTOL’s times.
(90, 4, 10.7, .15p) Grain a bit better than XTOL. Add 30% to XTOL’s times.
(90, 4.1, 9, .2d) Matched XTOL; a promising clone.
(60, 7, 11.5, .15p) This is Instant Mytol, by Jordan Wosnick.

Advice to Designers of Developers

Crystallization in a concentrate means it is collapsing as some chemicals go out of solution. It first appears as crystals on the bottom of the bottle, or as white smoke-like wisps in the liquid. It often continues until the liquid has separated into a cream and liquid. At first I thought that a high concentration-ratio (powder-weight divided by liquid-volume) was the primary cause, but further experiments disproved that. My latest experiments indicate that a major factor is the M/A ratio. D316 is barely stable, and its ratio is .489 (2.2/4.5). Mocon appears to be more stable, with a ratio of .429 (1.8/4.2). Dimezone S reduces the threshold-ratio a bit, and that’s why the borderline D316 cannot use Dimezone S. I suspect that reducing the M in D316 to 2.0g (from 2.2g) would reduce the ratio enough for it to be stable with Dimezone S. That change would give D316 an SMAP of (45, 2, 4.5, .08d/.05p), and my few tests of the Phenidone-version of this show that it’s a good developer. The .489 is not a hard limit. I had a stable concentrate with ratio .533, but its concentration-ratio was lower, so that’s a factor also. If crystallization is going to occur, I’ve always seen it within two weeks stored at room-temperature. Interestingly, substituting some (but not all) of the M with TEA (Triethanolamine) makes a concentrate more prone to crystallization, despite the low M/A ratio. TEA and sodium metaborate don’t get along in a glycol-based concentrate.

“PC” developers are those which use Phenidone or Dimezone S in combination with ascorbic acid or sodium ascorbate. The major problem with PC developers when mixed into water is the catalytic Fenton reaction, in which iron and copper impurities slowly destroy all the ascorbate. This is true even if using distilled or DI water, because the iron and copper come from your own chemicals. With a high quantity, it’s been reported that substantial ascorbate-loss can occur within one hour. XTOL uses DTPA-Na5 as a sequestering agent to remove these metals, and you can too if you can find some DTPA-Na5. Or you can create a concentrate using propylene glycol or TEA. No water means no Fenton reaction. But the ascorbic acid in these concentrates slowly oxidizes, causing them to turn shades of yellow and then shades of orange. At room temperature, they seem to last about 6 months without excessive ascorbate-loss. However, I have found that glycol-based concentrates can be stored chilled or frozen with no precipitation, so I strongly recommend doing so. I suspect they’ll last years in the freezer.

All the concentrates described in this article take advantage of these discoveries that I’ve made:

  1. Sodium metaborate dissolves into propylene glycol. Ordinarily, such an inorganic salt does not dissolve into an organic solvent, but this is an exception because borate esters are formed (Gerald Koch realized that this is the reason). Actually, Paul Verizzo discovered this and posted it to apug a few years before I did. The same happened with PC-Sulfite. See the pattern? The motto of my work seems to be “go where others have gone before”. :-)
  2. Crystallization does not occur if the metaborate/ascorbic ratio is at or below .489 (a little lower for Dimezone S).
  3. Precipitation does not occur in glycol+metaborate+ascorbic concentrates when chilled or frozen.
  4. Dissolving some sodium metaborate into propylene glycol increases the amount of ascorbic acid that can be dissolved. Or it at least makes it easier for ascorbic acid to dissolve. This fact allows the concentration to be high. Using Mocon as an example, when you pour the ascorbic acid into the solution, it’ll seem impossible that such a large amount of powder could dissolve in that small amount of liquid. But it will. In fact, there seems to be no solubility-limit. That, plus the fact that freezing produces no precipitation, tells me that ascorbic acid is combining with propylene glycol in some way, as also occurs with sodium metaborate. This is not simple dissolution.
As noted before, using Phenidone in a glycol concentrate boosts fog by a film-dependent amount. Neither chemical alone boosts fog, so something about the combination of Phenidone and propylene glycol together is causing the fog. That’s a reason to use Dimezone S. Also, Dimezone S is less prone to hydrolysis in water, but this advantage does not matter with glycol- or TEA-based concentrates.

If you are designing your own developer, be sure to test T-Max 100 (TMX) and Delta 400. TMX has an unusually early shoulder with many developers, and you’ll want to know where your dev puts it. Delta 400 can easily get a soft toe, so keep an eye on that one as well, comparing the toe with that from a common developer such as D-76 or XTOL. I suggest testing all B&W films made by the big-three makers (Ilford, Kodak, Fuji). These are only 11 films, and it only takes a few weeks to test all of them.

A factoid that’s nice to know: When dissolving the MAP chemicals into propylene glycol, the volume of the liquid in ml will increase by about 0.6 times of weight of those powders in grams. This lets you predict the volume of the resulting concentrate.

And my final bit of advice to designers of developers: Get a densitometer and a Stouffer step-wedge. It’s the only way to know what your dev is doing around the toe, where and how quickly it shoulders off, and if there are any anomalies in between.


I’d like to express my gratitude to the members of apug who have helped me learn about developers and answered my many questions. Special thanks should be given to Ron Mowrey (Photo Engineer, PE) who has tutored me from when I knew almost nothing about all this, and to Alan Johnson who has tried some of my developers and run experiments that I would not have thought of, producing valuable results.

Whew! Now that this project is over, I’ll have some spare time to do some shooting.

Mark Overton, 2013-4-6