Is there a chemical way to increase contrast in RA4 printing?

[coisasdavida]

Hello all,

I've been reading around and only found something about peroxide, which I know it is not what I'm looking for.

Can I add alkali? Change temperature and time? Any ideas?

Regards,
Gui

 

[hrst]

Increasing pH by adding hydroxide should work to some level. Increasing time or temperature works, but maybe not that much.

I've needed a little bit more contrast in some occasions, and increasing dev time from 2 minutes to 3 minutes gave me that. Probably adding more time would start adding fog thus decreasing contrast. You might want to reduce exposure a little bit at the same time.

 

[Mike Wilde]

Unsharp B&W mask, reversal processed, is how I have gone about it when I was really desperate, because it is a lot of work. I have cut contrast by adding citrazinic acid to the developer. I have never tried going the othere way to add contrast chemically.

 

[David Grenet]

You can add Hydrogen Peroxide or Cobalt Hexammine Chloride to your colour dev, but it will have a very limited lifespan once mixed.

You can bleach bypass (substitute a colour fix for the blix) but you will lose saturation.

Or, you can bleach bypass, wash, rehalogenate with a ferricyanide/bromide bleach and then run through the process again, blixing when satisfied with the result.

All of these have been discussed before: I suggest the search function if you want details because I haven't tried any of them and don't remember quantities etc off the top of my head...

Happy experimenting and please do report back on your results.

 

[JS MD]

hydroxide will increase D Min -

 

[coisasdavida]

Thank you all for your inputs!
I guess since peroxide and roller transport don't go together very well, I might have to give up roller transport and go back to rotary tube in order to try the peroxide thing.

Best regards,
Gui

 

[brucemuir]

Thank you all for your inputs!
I guess since peroxide and roller transport don't go together very well, I might have to give up roller transport and go back to rotary tube in order to try the peroxide thing.

Best regards,
Gui

I use trays for ALL my Ra4 and it works great.

I guess oxidation could be an issue with peroxide but no more than rotary I would think.

 

[anikin]

Well, I had a crazy idea for contrast control with roller transport. What about if you were to presoak the print in an accelerator (KOH or peroxide) and then run it through the processor? I've done it with SLIMT technique to reduce contrast, but I wonder if it would work in the other direction? Any experiences there?

 

[coisasdavida]

@brucemuir My idea of using rotary was to loose as little chemistry as I could with the peroxide. My guess is that I can process an 8x10" with 100ml in a rotary tube, but I'd need at least 350ml on a tray to get it covered. This is based on my readings that tell me that the peroxide will ruin the chemistry after a few minutes.

@anikin Wouldn't that contaminate the 3 gallons of chemistry inside my Colex?

 

[Bob-D659]

70 ml works just fine for an 8x10 in a Beseler print drum.

 

[anikin]

@coisasdavida, yep that worries me too. That's why I asked the question. 3 gallons you say? Ouch, the experiment might prove expensive. I'm with Bob then. The print drum sounds like a better solution.