I have some interesting results below.
You might remember that a year ago, with much help from PE and others, I created an XTOL-quality concentrate which I called "Mocon". The article for it is here: (there was a url link here which no longer exists) And then I vanished for a year, because I invented a better way of designing software, and ended up writing a book about it ("The IDAR Method") and presenting it at conferences.
I've kept a bottle of Mocon in the freezer over the year. This weekend, I used it to develop two rolls -- Tri-X and T-Max 400. Also, for the last 1.5 years, I've kept partly-full bottles of the similar D316 in the refrigerator and freezer, opening both for a couple of minutes once a month to simulate occasional usage. Here are the results:
* Mocon: Concentrate shows no evidence of yellowing or precipitation/crystallization, and the rolls came out perfect! Dense leaders and perfect negatives.
* D316: Both bottles (refrigerated and frozen) show no evidence of yellowing. However, a third bottle that's been frozen the whole time has a little crystallization on the bottom (Mocon had none).
In comparison, glass bottles of similar concentrates that were kept at room-temperature gradually turned yellow and then red over a period of months, even when they had not been opened. From this, I conclude that the yellowing is not caused by aerial oxidation. Also, when these bottles were opened, I heard a puff-sound of gas being released, and they started bubbling a little. When shaken, they bubbled furiously, as if they were carbonated. Clearly, at room-temperature, one or more reactions occur over a period of months which produce a gas and the yellowing. It's interesting that refrigeration appears stop this reaction and not merely slow it down.
My conclusion: Based on its potency and observed rate of yellowing (none), I'd say Mocon will last years when kept frozen. I recommend it for those doing occasional shooting who want XTOL-quality.
Mark Overton
You might remember that a year ago, with much help from PE and others, I created an XTOL-quality concentrate which I called "Mocon". The article for it is here: (there was a url link here which no longer exists) And then I vanished for a year, because I invented a better way of designing software, and ended up writing a book about it ("The IDAR Method") and presenting it at conferences.
I've kept a bottle of Mocon in the freezer over the year. This weekend, I used it to develop two rolls -- Tri-X and T-Max 400. Also, for the last 1.5 years, I've kept partly-full bottles of the similar D316 in the refrigerator and freezer, opening both for a couple of minutes once a month to simulate occasional usage. Here are the results:
* Mocon: Concentrate shows no evidence of yellowing or precipitation/crystallization, and the rolls came out perfect! Dense leaders and perfect negatives.
* D316: Both bottles (refrigerated and frozen) show no evidence of yellowing. However, a third bottle that's been frozen the whole time has a little crystallization on the bottom (Mocon had none).
In comparison, glass bottles of similar concentrates that were kept at room-temperature gradually turned yellow and then red over a period of months, even when they had not been opened. From this, I conclude that the yellowing is not caused by aerial oxidation. Also, when these bottles were opened, I heard a puff-sound of gas being released, and they started bubbling a little. When shaken, they bubbled furiously, as if they were carbonated. Clearly, at room-temperature, one or more reactions occur over a period of months which produce a gas and the yellowing. It's interesting that refrigeration appears stop this reaction and not merely slow it down.
My conclusion: Based on its potency and observed rate of yellowing (none), I'd say Mocon will last years when kept frozen. I recommend it for those doing occasional shooting who want XTOL-quality.
Mark Overton