Pyro and Pyrocatechin developers

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Recently, there has been a strong re-emergence of the Pyro and Pyrocatechin based developers spurred by Gordon Hutchings’ PMK, Sandy King’s Pyrocat-HD, John Wimberley’s Pyro based WD2D and Barry Thornton’s Pyrocatechin based Dixactol Ultra commercial developer.


- Tanning/staining developers have advantageous properties including high acutance and local contrast control.
- Pyro and Pyrocatechin act as a hardener in the gelatin (they tan the gelatin). This has a two fold advantage. Firstly it helps solidify and protect the film emulsion in films like EFKE where the emulsion is thicker and/or softer and more prone to damage. Secondly, by decreasing the movement of developer agents through the hardened emulsion, acutance is increased and therefore apparent sharpness of the image. Where the developer exhausts itself quickly, it is not replaced by local developer within the hardened gelatin, only by fresh developer during agitation. Boundary contrast is increased giving this higher apparent sharpness seen in many negatives developed in Pyro(catechin).
- The tanned gelatin also stops the movement of dissolved silver, lessening the re-plating action of the Sodium Sulphite. This keeps the grain nice and sharp.

Contrast control
Pyro and pyrocatechin developing agents oxidize rapidly where they are most active, and this oxidization leaves a beneficial stain in the negative image; the effect of which is a natural controlling of the contrast. This oxidization is generally in the highlight areas of the image as that is where most of the developer activity occurs. Therefore, the stain is exactly where we need it. In “Develop for the Highlights”, I explained that when taking black and white photographs we generally expose for the shadows and try to bring down the highlights during the development process. Pyro staining can really help us here. During printing (enlargement) of the negative the stain automatically controls the highlights whilst allowing the mainly unstained shadows to come through unhindered.

Here I list Barry Thornton's Pyrocatechin Two Bath developer, possibly the pre-cursor to his remarkable Dixactol commercial developer.

Bath A Stock solution:
Pyrocatechin 10g
Sod. Sulphite 2g
Pot. Bromide 0.5g
Water to make 100ml

Bath B Stock solution:
Pot. Hydroxide 10g
Pot. Bromide 0.5g
Water to make 100ml

Working solutions of A and B are mixed 1+14 with water.  Recommended times are 4 minutes in A at 21° C with agitation once every 30 seconds, followed by 4 minutes in B at 21° C with agitation once every minute. Do not rinse between baths.

Sandy King has suggested that replacing the Pot. Hydroxide with 40g of Pot. Carbonate could improve this developer by making it slower working and finer grained.

Both this and
Pyrocat-HD are good staining developers and produce a stain that is very compatible with Multigrade and other VC papers. However, the new king of this castle is 510-pyro. This developer has all of these benefits and more.