Bergger PMK Roto Additive

[Tim V]

Hi all,

Anyone know what Bergger PMK Roto Additive is? I'm assuming that it's an antioxidant of some sort, buy anyone know what and how it'll effect film development times etc. when used in the Jobo?

From the Bergger literature, per Linhof Studio's website:

"The Bergger PMK Roto Additive was formulated in order to allow the use of the PMK in the Jobo-type rotative machines. It may be used between 1+50 and 1+100, and must be added to your PMK working solution. Developing times given on the PMK datasheet can be used, but they are only a starting point. You will certainly have to adapt them in order to reach the result you expect."

I'm going to try it with a box of Pancro 400 to see how I like PMK in the Jobo vs Pyrocat-HD mixed 2:2:100. I'll certainly need to still split the developer stage into to 1L baths, but just wonder how much more active it might make the developer and hence what time differences to expect.

Any info / guidance / user experience appreciated!

Thanks,

Tim

[Tim V]

PS: I’ll add that I believe I’ve asked a similar question to this before on this forum, but from memory then no one had experience with this premixed product from Bergger. Perhaps that has changed now?

[Pere Casals]

I don't know what antioxidant it is, but the typical antioxidant for PMK (etc) is Ascorbic Acid.

Basicly Rollo Pyro is PMK with antioxidant: Ascorbic.

The ascorbic acid also works as a silver developer, so the Rollo formula has less Metol regular silver developer and more staining developer (Pyrogallol), I guess to compensate the stain vs silver levels.

http://jeffreysoper.com/node/124
http://jeffreysoper.com/node/125


You should find the Roto additive chemical safety datasheet (MSDS, PSDS, SDS), but if the additive is Vitamin C related perhaps there is no hazard information, I don't know if cheap food grade Vit C requires a warning information.

In any case you may add regular Ascorbic Acid for a similar effect.

Ascorbic Acid decreases the Solution A shelf life, but you may just add the ascorbic dose in the working solution just before usage, just use the calculator.

The antioxidant effect is to lower the general stain level, you may simply add say the half of the ascorbic acid dose that you have in Rollo to the PMK and see the starting point, the more ascorbic acid you throw the less general stain, but also you should have some less stain vs silver density, in the Rollo more Pyrogallol dose is used to compensate that, I guess.

[Doremus Scudder]

I'll augment Pere's response with some practical observations. Sandy King described a technique, in which he added ascorbic acid to Pyrocat. I thought a similar addition to PMK might help with expansion developments, so I played around with it a bit, with Rollo Pyro in mind.

My preliminary tests were with PMK diluted 2:4:100 (double strength) with ascorbic acid added to make 0.1g/l (I added 5ml of a 5% solution to 500+ml). For ease of use, I mixed a 0.5% ascorbic acid solution, i.e., 0.5g in 100ml of water, and used this as my “Stock C” solution. (I used a 500mg tablet in 100ml water, then filtered, you could do the same or use food grade ascorbic acid.) The final mix, then, was 2 parts A, 4 parts B and 1 part "C" added to 100ml of water (2+4+1+100), e.g., 10ml A + 20ml B + 5ml "C" + 500ml water to make 535ml total.

This "PMKC" formula resulted in more and greener stain than PMK in normal dilution. The negatives seemed to be quite printable and the potential for expansions was definitely there. I still need to refine my times for N+ developments with this mix.

I would think that you could use this as a starting point for using PMK in rotary development as well. The ascorbic acid should give enough protection from over-oxidation for all but the longest development times. You'll have to test for times, of course.

Hope this helps,

Doremus

[koraks]

>This "PMKC" formula resulted in more and greener stain than PMK in normal dilution
Sounds like more oxidation, not less.
I think it's a lot of guessing to figure out what antioxidant would be in the Bergger product. Could be ascorbic acid/ascorbate, could even be HAS or something else entirely. Whatever it is, it shouldn't impede staining altogether which makes ascorbate a possible candidate, but I'm sure there are many others.

[Tim V]

Thanks so much for the replies, guys. It's all good information and while I don't know what is actually in this Bergger product, it must not be much because it only costs £5 per 250ml bottle!

I've been having some great results with Pancro 400 and HP5+ souped in Pyrocat-HD in the Jobo – I'm especially liking the Pancro now that I've settled on times – but I've realised that at the printing stage with VC papers I prefer the stain of PMK (I used to use it in trays, one sheet at a time, but switched to Pyrocat when I got the Jobo.) I like PMK's subtle highlight compression for what I do, although in all other categories Pyrocat is at least the equal of PMK it seems. Anyway, I'm off topic and this is old news.

This Bergger product is recommended to dilute 1+50 to 1+100 with the working solution and I'm wondering to what extent it might change the standard developing times as indicated in the product writeup. If the time for normal PMK (no additive) is 18mins at 20 degrees with normal agitation – you have to agitate quite a bit with PMK in my experience, almost near constantly – then I'm wondering if reducing this by 10% might be a good starting point. In other words, is it more the rotary system that will affect the time and less the additive solution, or the other way around?

Either way, even with the additive I will certainly split the developer stage into two 1L baths to be extra sure excessive oxidisation doesn't take place.

Thanks again.

Tim

[Chauncey Walden]

Gordon Hutchings recommended adding 5ml/l of a 10% solution of EDTA for rotary PMK. This is what I have always used and found no need to split the developer or change the time.

[Drew Wiley]

EDTA is marginally useful if you can't control streaking in any other manner. A slight linear rocking of the drum in addition to rotation is a better way to do it.