Pyro: Some Truthful Informaion About Health Considerations    

Dunno if this is the best place but I figured this is the best place as I have a feeling many LF'ers develop their own. Recently read an article from an UK photo mag. Guy basically cannot figure why anyone would risk death?? to use PMK when the gains are so minimal? Opinions?

Here is a response by Richard Knoppow

You can get Material Safety Data Sheet from the internet. Try the SIRI site at http://hazard.com

Pyrogallic acid is toxic but one must be careful in interpreting MSDS: mostly they are written for industrial users of substances who use and store them in very large quantity.

Pyro is a sensitizer and can cause very strong skin reactions. It should be kept out of the eyes for the same reason. It is capable of causing life threatening damage if ingested in fairly large quantity. It will irrate the lungs and respiratory system if inhaled. Pyro can penetrate the skin but so can many other substances used in photography.

There have been NO studies of the chronic effects of Pyro exposure. Pyro is no more hazardous than several other developing agents. It should be treated with respect but there is no unusual hazard in using it.

Since airborne Pyro is dangerous to breath in its wise to mix Pyro developers while wearing a dust mask and facial protection. You should wear nitrile gloves. Try to avoid getting the stuff into the air. It is in light flakes which become airborne easily so some care is needed.

Mixed Pyro developers are only moderately hazardous but its a good idea not to get your hands into it. Use nitrile gloves (latex is not good enough and some people are sensitive to latex). You don't need a dust mask to use the mixed developer, it is only the airborne flakes which are hazardous. Another reason for using gloves is that Pyro produces a very persistent brown stain on anything it is on when exposed to the air including your hands and cloths.

As far as the value of Pyro developers, that is rather controversial. Some photographers think it is magic, others see no special virtue in it.

Pyro, in formulas like PMK and the traditional ABC type create an image wise stain which acts to intensify the image when printed with blue light. Most graded printing papers are sensitive to blue light only so the Pyro stain appears opaque to them. Variable contrast papers are sensitive to green as well as blue but the green sensitive component produces lower contrast than the entire emulsion. When printed using a Pyro negative the stain acts as a selective contrast filter. Since the stain is denser in the highlights it tends to reduce the contrast there yielding something of a compensating effect. The degree to which this happens depends on the particular paper and the nature of the stain. The spectral transmission of the stain, and its visual color, vary with the emulsion and with the developer formula, so there is no certain result of using it.

The idea that the stain image masks grain is probably not true although widely believed.

Pyro also differentially hardens the emulsion in proportion to the density. The hardening follows the stain. This effect is strongly affected by the nature of the emulsion. The effect is probably negligible on modern emulsions, which are made very hard in manufacture. When the differential hardening effect does take place it can result in a strong edge or border effect because it will change the rate of diffusion of the developer, and its reaction products, through the emulsion. In older emulsions this could result in the strengthening of the contrast at the borders between high and low density areas. This increased edge contrast is interpreted by the eye as sharpness, an effect called "acutance". Similar effects can be produced by non-Pyro containing developers.

Pyro was the first organic developing agent, discovered by simultaneously and independently by Fredrick Scott Archer and von Regnault in 1851. For several decades it was the most widely used developing agent of all. Then other agents, particularly the combination of Metol and Hydroquinone, displaced it for nearly all uses. Metol or Metol-Hydroquinone developers are, in comparison to Pyro, more reliable and more predictable.BTW, Hydroquinone is closely related to Pyrogallic Acid but was not discovered until 1880 (William de Wivelsley Abney).

So, I don't know whether you would find PMK or some other Pyro formula worth while, but there is not really any special hazard to mixing or using it.

Richard Knoppow Los Angeles, CA, USA