Mixing Pyrocat HD

Mixing Pyrocat HD

Pyrocat Versions and Mixing Directions
by Sandy King, March 2010

Below are mixing directions for various versions of Pyrocat, including DHD, -M, -P, -MC and -PC. I am indebted to Pat Gainer for his advice and recommendations for mixing the glycol based versions of Pyrocat, including Pyrocat-HD, -MC, and -PC.

Pyrocat-HD is the original Pyrocat formula and is still the most popular judging by sales and questions I get about it. The other formulas, which include Pyrocat-M and Pyrocat-MC, and Pyrocat-P and Pyrocat-PC are recommended primarily for rotary processing, where they tend to give slightly greater acutance than Pyrocat-HD.

  • HD: High Definition
  • C: Vitamin C (Ascorbic Acid)
  • M: Metol
  • MC: Metol + Vitamin C
  • P: p-Aminophenol
  • PC: p-Aminophenol + Vitamin C

All of the Pyrocat formulas are acutance developers that give good pictorial rendition when used at dilutions of 1:1:100 to 2:2:100 with normal agitation. When used at higher dilutions with reduced agitation they become high acutance developers with very pronounced adjacency effects.

Some of the characteristics of all of the Pyrocat variants are:

  • Good acutance.
  • Tight grain pattern.
  • Lower levels of general stain, even with long development times, than most pyrogallol based developers.
  • Does not cause uneven staining or streaking when developed in Jobo.
  • Use with dilute solutions and minimal agitation for very adjacency effects and enhanced sharpness.
  • Very inexpensive to use.
  • Stock solutions last a long time.¬†A year when mixed in water, and several years if (A) is mixed in glycol.
  • All of the Pyrocat versions use the same Solution B, which is a 75% solution of potassium carbonate.

It is possible to substitute a 20% solution of sodium carbonate, but if you do so, the working formula must be mixed at 5X the amount of Solution B. Thus, a dilution of One Part A + One Part B + 100 Parts water when using the 75% potassium carbonate solution would become One Part A + Five Parts B + 100 Parts water.

Distilled Water750 ml
Sodioum Metabisulfite10g
Potassium Bromide1g
Distilled water to make1000ml
Distilled Water700 ml
Potassium Carbonate750g
Distilled water to make1000ml

To make a standard working solution mix 1 part A with 1 part B with 100 parts water. *Or substitute 25 grams of metol (with slight loss in film speed)

Pyrocat HD Formula

Pyrocat-HD is mixed as two stock solutions that are diluted to make a working solution for developing. The shelf life of the stock solutions is very good. Stock Solution A can be stored in partially full bottles for up to a year, while Stock Solution B keeps indefinitely.

Mixing The Stock Solutions


1. Start with 750ml of distilled water.
2. Add 10g of sodium metabisulfite and stir until dissolved.
3. Add 50g of Pyrocatechin and stir until dissolved.
4. Mix 2.0g of Phenidone with about 5ml of isoprophyl alcohol and stir into an even paste, then add to the stock solution and stir until dissolved.
5. Add 1.0g of potassium bromide and stir until dissolved.
6. Add distilled water to 1000ml.


1. Start with 700ml of distilled water.
2. Weigh out 750g of potassium carbonate* and add the chemical very slowly to the water, with constant and rapid stirring. If you add the solution too fast, or don’t stir enough, it will be impossible to dissolve all of it in the water. As you add the chemical an exothermic reaction takes place and the solution will warm up appreciably.
3. Add distilled water to 1000ml.

* Potassium carbonate is deliquescent, which means that it will absorb water from the air. It must be stored in sealed containers to prevent this from happening because if you weigh out 100g of potassium carbonate that has absorbed a lot of water the actual chemical weight might be only 60-80g, which of course would produce a much weaker B solution than the formula requires.

Working Solutions Of Pyrocat HD

For developing negatives intended for printing with silver gelatin papers the recommended working solution is a 1:1:100 dilution. One Part Stock Solution A + One Part Sock Solution B + 100 parts water.