Pyrocat HD and Dimezine S

[Richard Wasserman]

I need to mix a new batch of Pyrocat HD and realized I am out of Phenidone, but I do have Dimezone S. Can I use Dimezone instead, and would I use the same quantity? Also, might the stock solution then have a longer shelf life because of Dimezone's greater stability?

Richard Wasserman

 

[craigclu]

I just checked some notes on an experiment from some time ago. Here's a paste from my spreadsheet showing I used a 1.4X factor for the Dimezone-S. I use a grain scale (firearms type) so that these small numbers are doable. I didn't do an extensive review of it but I recall it seeming just slightly less active than the HD. I believe it was Gerald Koch who had made a comment regarding the factor to assume between the two?

Propylene Glycol 150 ml
Sodium Metabisulfite 2 g
Pyrochatechin 10 g
Dimezone-S 0.56 g
Potassium Bromide 0.2 g
Propylene Glycol to 200 ml

Someone once commented that there is no shelf life advantage in this application vs water based uses.

 

[john_s]

I have been using Dimezone-S instead of phenidone and I have collected some opinions from posts on the web. Firstly, on a molecular weight basis, the amount of Dimezone-S, being a heavier molecule, should be 1.27 times the weight of phenidone in a formula.

Furthermore, there are some posts that suggest that a bit more is in order since the dimezone-S has lower activity even when adjusted for molecular weight. How much more? There are no actual measurements that I could find, but some say no increase and some suggest something like another 25%.

However, it might not matter. Here is a quote from Sandy on the subject of using Dimezone-S in Pyrocat HD, copied from APUG some time ago:
<start of quote>
The amount of phenidone in the Pyrocat-HD formula is not as critical as one might think. In my own tests I have seen very little difference with amounts ranging from 1.5 g per liter to 2.5 g per liter of Stock Solution A. The minimum amount appears to be about 1.0 g, and the maximum about 3.0. Below 1.0 g there is not as much synergism (= longer development times) and above 3.0 g there is an increase in B+F.

I have no experience with Dimezone-S. However, as others have suggested, phenidone in powder form lasts a very long time. And once mixed in the Pyrocat-HD stock solution the useful life is at least six months in a partially full bottle. And if you need more shelf life out of the Stock Solution A consider mixing it in propylene glycol instead of water, which should increase its life to years instead of months.

Sandy
<end of quote>

My guess for Pyrocat HD was 2 x 1.27 x (a bit more) = 3g

It seems to work very well. Fog is not noticeable, but I haven't measured it. I use VC paper.

 

[Richard Wasserman]

Thanks Craig and John for the information. I'll mix up a batch of Pyrocat HD tomorrow using Dimezone S and will try it on some unimportant film. It sounds like it should work very well.

Richard Wasserman

 

[john_s]

I forgot to mention that a benefit of Dimezone-S in place of phenidone is that it dissolves reasonably well in aqueous solution, without having to resort to tricks like other solvents such as alcohol.

 

[srs5694]

Aren't there two (maybe more) forms of phenidone that vary in solubility? I seem to recall running across references to this; I believe the variants were referred to as phenidone A and phenidone B. At least one retailer (Digital Truth) refers to their phenidone as "phenidone A." I don't recall whether this was the version that dissolved more or less easily, though.

 

[john_s]

There is also one called Dimezone (without the -S).

Referring to CAS numbers would seem to be the most reliable method of identification.

I think that Ryuji Suzuki's site has some comments about some aspects of the different forms of phenidone, including solubility and stability in aqueous solution. Look in his formulas for developers.