Much of the current interest in the use of Pyro is due to Gordon Hutchings’ PMK formula, first introduced to the public in a long article in View Camera in September/October 1991 and since promoted in The Book of Pyro, first published in late 1991. Hutchings describes PMK as a universal developer for modern film emulsions used under diverse conditions, easy to use, and designed to achieve maximum image stain and minimum general stain. During development in PMK a yellowish-green image stain is produced in those areas of the negative where silver is being reduced, and this stain is proportional to the amount of silver: least in the shadows where there are areas of low silver density, greatest in the highlights. Since the exposing light sees the stain as increased printing density, total negative density is equal to the combined silver and stain densities. The result is that the stain masks film grain by filling in between silver grains, resulting in both increased acutance and finer tonality in the final print. This effect is seen in negatives of all sizes but the impact is particularly dramatic in 35mm and roll film formats. Steve Simmons describes this effect as follows: “In other words, there is no general overall stain that would act like fog, but a stain that acts like extra density and this stain increases as it goes up the tonal scale. Consequently, the film’s high value silver densities are thinner than with a conventional developer, and the extra density needed to produce the high value tones is created by stain. These ‘thinner’ high value densities in the negative can produce wonderfully clear delicate high values in the print, unlike any tone that can be produced by a non pyro film developer.”³