Question About Mixing Pyrocat-HD

[thronobulax]

I've just completed mixing my first batch of 500ml each of Parts A&B Pyrocat-HD in water.

As expected, mixing B is noticeably exothermic and took a while for the Potassium Carbonate to fully dissolve.

What was unexpected was that the final/complete mixture of Part A had some precipitate in it that was resisting going into solution. It was a very small amount of dark brown precipitate, which I crushed as best I could but still didn't get completely into solution.

My "fix" was to place the mixing container for Part A into a tempering bath filled with water around 50C to raise the chemistry to the point I got most all the precipitate into solution.

Is this normal? Should I have mixed the Part A in heated water in the first place? Sandy King makes mention of elevated temps when working with Glycol but I found nothing to suggest this for the water-based formula, which is why I wonder ...

 

[mpirie]

Yes, you should mix with water at around 50 ˚C.

Mike

 

[Alan9940]

What Mike said. I've always mixed all my chemistry--except Amidol for print development--at about 50C.

 

[Camerashy]

I asked a question about mixing part B on The Large Format Photography Forum but it was not answered to my satisfaction. However I did find an old post that enlightened me. I wanted to know about mixing part B by adding the dry chemical amount.
For instance,
800ml water
10ml part A
7.5g pot. Carbonate (anhy) (stir till disolved)
Top up to 1ltr
Or
800ml water
10ml part A
10g sod.carbonate (mono) or 23.1g washing soda (crystal)
Top up to 1ltr
I have not tried this yet but can anyone see why it would not work?

 

[Ian Grant]

Part B should be:

Potassium Carbonate 750g
Water to 1 litre

Then us 1A+2B to100 water


If you use Sodium Carbonate (anhyd) then due to it being less soluble but also slightly more alkali:

Sodium Carbonate Anhyd) 500g
Water to 1 ltre

Then us 1A + 2B to 100 water

Ian

 

[Camerashy]

Ian you have just supplied yet another variation for solution B.
I thought the original formula was 750g pot. Carbonate in 1000ml distilled water.
Use 1a+1b+100 for normal tank inversion
2a+2b+100 for rotary and sheet film in trays
1a+1.5b+100 for added contrast in paterson tanks
Part B sodium carbonate (mono)
200g in 1000ml
Use 1a+5b+100

Guess I have some experimenting to do once I can get out of the house. It is not much fun being in lockdown looking out of the window at the non stop rain.

 

[Ian Grant]

When Sandy King first published Pyrocat HD it was with Sodium Cabonate (anhyd) 500g in 1 litre of water and 1 + 2 to 100 in fact Peter Hogan was selling it as Prescysol and using Sandy King's instructions. Soemeone suggested using Potassium Carbonate (anhyd) instead due to it's greater solubility and he change the Formula.

If you use Sodium Carbonate (mono-hydrated) the you'd need to use 230g (not 200g) per litre in PArt B for use at 1A + 5B to 100 water, I use de-ionised water for Parts A & B.

Ian

 

[Camerashy]

Thank you Ian, that explains a lot about all the different solution B mixes and ratios I have come across on the net. Good to get an accurate starting point. At what temperature do you have your water when dissolving the carbonate?