Thursday, July 24, 2008

Pyrocat HD


I have been using Pyro as a developer on and off for 2 years now and until now have relied on a prepackaged kit supplied by Retro Photographic in the UK. I have no complaints with the kit but its formulation is not public and if I am to undertake further refinement of the process I feel that I need full control and continuity of supply so I have concluded that I should mix my own brew. However there are so many competing formulae.

I have not tried any of them and do not know if the Retro Formula is derived from any particular published recipe.

I have therefore decided to follow the suggestion of The Unblinking Eye and start out with Pyrocat HD.

I therefore ordered the required raw chemicals and mixed away. The top photo shows the set up. I used the utility room away from food etc and equipped myself with latex gloves and a dust mask.

Pyro is mixed as 2 concentrates which are finally diluted and combined just before use. The dilute developer does not keep and oxidises quickly to a brown mess. The B concentrate has only one chemical Potassium Carbonate which is relatively innocuous. So I started with it.

In practice I decided to halve the recipe. This is fraught with some difficulties because some of the weights are quite small but 500ml is a lot of developer when you consider that 4 sheets of film only take about 150ml solution at a 1:100 dilution.

The instructions are first class. Potassium Carbonate is not that easy to get into solution so I used a large bowl and added chemical 1 teaspoon at a time and stirred like mad. Once dissolved it went back into the measuring cylinder to be topped up to 500ml. The result is above. Not I used de-ionised water not tap water to make the concentrate. I have had no problems using the tap water here for developing so plan to use it to dilute to working strength.




Gaining confidence I set off on concentrate A.

The photos show the packs of chemicals and the small chemical scales. These are said to be accurate to 0.1g. That is quite tight since the formula requires on 0.5g of Potassium Bromide. The mixing went without hitches. These chemicals dissolved quickly, even the phenidone which has to be mixed first with Isopropyl alcohol.

The formula and instructions are at The Unblinking Eye

NB in the UK Pyrocatechin is known as Pyrocatechol

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