View Full Version : PMK... active life in an open tray?

kev curry
26-Mar-2013, 13:00
How long will it be good for in an open tray? Could I be safely developing 8x10 one at a time over the course of a few hours in the same batch of PMK?


Kirk Gittings
26-Mar-2013, 13:19
My experience with a few pyro developers (PMK included but mainly Pyrocat HD) is that they oxidize very quickly and must be mixed just before development.

Drew Wiley
26-Mar-2013, 13:29
I seriously doubt it. I wouldn't even want to try over half an hour - not that I've personally tested this, but am basing this
on something Gordon Hutchings wrote way back when he he first cooked up the formula.

Brian C. Miller
26-Mar-2013, 13:56
PMK, and similar, is a one-shot developer. Mix just before use, and discard when development is completed. The developer is one of the cheapest, and the concentrates will last a long time.

bob carnie
26-Mar-2013, 14:02
We try to process within minutes, don't ask why I know waiting a long time can be a problem.

kev curry
26-Mar-2013, 17:02
The PMK was still good after doing 3 negs individually one after the other. All 3 were developed for 17 min each. Contrast looks consistent across the 3 negs. I know Hutchings mentions about the oxidation in his book but I couldnt find the page. No matter alls well that develops well.

Doremus Scudder
27-Mar-2013, 03:28

I've had used PMK go bad sitting in a tray for slightly less than half-an-hour. That doesn't mean that it lost all its activity, but that the negatives developed in the older developer were thin/less contrasty. Fortunately, they were just test negs that I was developing after a run of three negs. Since I usually develop 6-8 at a time, I figured I could develop the test negs (focus tests) in the used developer and save the mixing time. While there was enough information on the negs for my test purposes, they would not have been fun to try and print.

This points to a problem with your proposed workflow. While I've had unused PMK seem fine after sitting in the tray for 15-20 minutes before I got around to developing (phone call...), once you have developed one or more negatives in a batch of PMK, the oxidization is really accelerated (mixing via agitation, chemical reactions, etc.)

However, it seems a waste to toss 2+ liters of PMK after developing just one 8x10 negative. So, I might suggest the following test (yes, it'll take some film...). Shoot three identical negatives (preferably of a scene that you like, so at least you won't waste all the film) and develop them in PMK together with four other negatives of anything you like as follows:

Develop the first of the three identical negs in the freshly-mixed developer. Now use the developer for a couple of other shots (since you mention that you've made it to three without adverse effects) then, as negative number four through this batch, develop the second of the identical negs. Compare and see if there is a significant loss in density/contrast (signs that the developer is losing activity). If so, stop there.

If all is well, develop three more other negatives and then, in place eight, develop the last of the three identical negs. Compare again. I doubt that the PMK will have lasted this long, but if it has, you have a method for developing eight 8x10 negs in 2 liters of PMK. If not, throttle back your process to the point where you can live with the reduced activity of the developer. And, keep an eye on the other negatives you are developing. If the developer dies before you get to neg 8, then quit!

You may find that you can compensate somewhat for lost developer activity by increasing development time (say 10% more for each additional negative... you'll have to test this too using identically exposed negs).

Anyway, with a bit of testing you should be able to determine how long you can use one batch of PMK and how much you need to adjust developing time to compensate.

Other ways to perhaps deal with the problem: Learn to shuffle and develop in batches (four negs at a time should be doable and I wouldn't exceed six 8x10s in two liters of PMK anyway). Use rotary processing and Rollo Pyro (a PMK cousin) and use less solution for each neg. Or maybe use PMK one shot in an 8x10 tray, and use as little solution as necessary for even development and agitation (you'd have to tray rock, which is not my favorite method of agitation, but there are many who use it successfully).

Hope this helps,


kev curry
27-Mar-2013, 06:17

Thats very helpful indeed. Thanks for your time and insight. I may just get around to using your method and testing this properly. I use tubes for 5x4 and always think to do the same for 10x8 but never got around to picking them up. I guess I prefer doing the 10x8 by hand one at a time for the guarantee of beautiful negatives. Its just the time factor that gets a little wearing. I shuffled 5x4 before tubes but have always opted to do the bigger sheets individually. I should probably just go ahead and try shuffling the big negs, it would solve a lot of issues really. Ive never been mad about film testing either, something else I should challenge knowing the learning that can be had along the way.


Chauncey Walden
27-Mar-2013, 07:45
I always use 350ml of PMK one shot per 8x10 when developing one at a time in a tray. A little EDTA as per Gordon might prolong the life of a larger volume for serial processing.

kev curry
27-Mar-2013, 12:08
I just read Hutchings in his ''The Book Of Pyro'' page 59 where he states that... ''PMK solution can be used in an open tray in excess of one hour without development problems''.

That was my experience last night.

Hutchings states that PMK will develop 350 square inches of film per liter which is 16 sheets of 5x4 or 4 sheets of 10x8 on the previous page.

Drew Wiley
28-Mar-2013, 13:54
I always measure out my water and let it come to correct temp equilibrium in the tray, along with all the other chem, but
have my A & B components measured out in separate graduates, and don't add them to the water until immediately before
my development session. Being careful in this manner, I've had 100% predictability with PMK - never and issue (except once
when I outright forgot to add it to the tray of water!)

Jim Noel
3-Apr-2013, 09:19
PMK, Pyrocat HD and other pyrogallpl and pyrocatechin developers are so cheap I think it is a big mistake to try to stretch their use. The first negative which is ruined by insufficient development will be the best image you ever focused on.

Brian Ellis
3-Apr-2013, 11:22
I used Michael Smith's formula. It lasted for 3-4 hours or so in a tray IIRC.

3-Apr-2013, 13:29
All of the two-part pyrogallol and pyrocatechol developers I am familiar with are designed to be used very soon after mixing Solution A and B with water. The working solution begins to oxidize after the working solutions are mixed, and will gradually lose working strength with increasing time. How fast they lose strength in an open tray depends on several factors, including the specific formula, surface area exposed to air, agitation, number of sheets that go through a specific amount of working solution, temperature, and probably other factors of which I am ignorant. However, if you did very close testing involving sensitometry with any of the formulas, for example using BTZS type testing, I am virtually certain that the results would be different if the solution is used just after mixing compared to four hours later.

Bottom line, all of these formulas are designed to be used shortly after mixing, and they do go bad gradually with time, dependent on the factors mentioned earlier.