Safety of Pyro : LUSENET : B&W Photo - Film & Processing : One Thread

In response to my concerns about the safety of using pyro in the home, an acknowledged writer on b&w processes indicated he thought it no more toxic than household bleach or exposing fingers to print developer. This came as a surprise as gallic acid is considered highly toxic. I would like to try pyro as I think from what I have seen published I would marginally prefer the look to Dixactol, a newer staining formulation which is possibly less toxic. I would be interested in other views on this. I would add I don't plan to drink it - I'm just concerned about spills drying to dust with an 18 month-old toddler around the house. Also, I would use pre-mixed PMK rather than mix it myself. What precautions do people take?

-- Nigel Craig (, April 23, 2001


Pyro is indeed toxic, and easily absorbed through the skin ; you should always wear gloves when handling pyro and avoid splashes. There is also a risk of breathing dust when mixing from powder, and the fumes from the oxidising liquid are not that pleasant. As long as you're careful, however, and clean up any spills thoroughly, and properly ventilate your working space, you should be OK.

-- fw (, April 24, 2001.

I agree that PMK can be used safely. I've been using it for nearly ten years now (since I first found the formula published in Camera & Darkroom). I have always mixed my own, wear a mask when mixing solution A, mix it outside where the fumes won't bother me, and have never had the slightest problem. I bought a box of surgical gloves to wear when developing sheet film, and always wash my darkroom sink down after developing. Nowadays I mostly use PMK for my medium format work and use Pyrocat-HD for sheet film, so I won't have to wear gloves. Pyrocat-HD was formulated by Sandy King as a substitute for PMK--I find that the development times are identical, the stain works the same way (though it's a different color), I can agitate only once per minute, and it's dirt cheap. I've heard very good things about Dixactol, but have an aversion to proprietary formulas (I'd be interested to compare its cost to hand-mixed PMK).

-- Ed Buffaloe (, April 24, 2001.

I, too, was somewhat "weirded out" at first about using "the most toxic chemical in the darkroom," as Gordon Hutchings puts it. But, as I use it, I realize I've always tried to avoid getting darkroom chemicals on me, and my normal procedures work just fine with pyro. I keep a damp rag nearby in case of mishap, and mop things up if needbe, rinsing out the rag in cold water as necessary. I also buy my PMK in liquid form from Photographers' Formulary to avoid inhaling any dust (which is potentially the most dangerous aspect). In short, the more I use it, the more I just treat PMK like any other chemical I don't want to get on me--NO BIG DEAL! And by the way, I don't think pyro is any more toxic than the selenium most of use for archival toning.

I would really encourage you to try PMK. Order Hutchings' book with your chemicals and save $5 or so on the deal, or read about PMK in the Film Developing Cookbook. I know some people on this forum haven't had good luck with PMK, but I certainly have. The stuff lasts forver and just gets better with age. My negatives have never been so consistent or easy to print, and the highlights seem to leap off the page! Good luck if you decide to give it a whirl.

-- Brian Hinther (, April 26, 2001.

Pyrogallo is toxic and is easily absorbed through the skin, but so is catechol, which is the primary ingredient in DiXactol and Pyrocat- HD. With that said, neither is so toxic that a few drops of developer solution on your hands will cause you any harm. Just don't be excessively careless about it. Don't sprinkle it on your cornflakes in the morning! But don't worry about incidental contact. The exposure levels that are truly dangerous would be something like immersing your hands in it on a daily basis for a full workday. You should be careful with the dust, however. Pyrogallo is particularly dusty, and you certainly should wear a mask when mixing the formula. Catechol is less dusty, but you probably should still show it the same respect. Inhaling the dust is a lot more dangerous than a few drops on your hands. If you tray process your film, wear gloves with either solution. Ted

-- Ted Kaufman (, May 27, 2001.

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