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  #1  
Old 23rd January 2022, 07:44 AM
John King John King is offline
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Default What are they playing at?

I have just read on a Photrio post where someone has added a small quantity of Hydrogen Peroxide to RA4 developer apparently trying to increase contrast and are highly surprised when all they get is a colour cast that cannot be dialed out.

Then there are all different suggestions to deal with that but apparently none that say the author is a buffoon, - Hydrogen Peroxide is a very dangerous substance even at weak solutions especially when used by a person who seems to have no expertise in dangerous chemical handling. (They got the idea off a You Tube Video - oh yes that's bound to be accurate! Any one with knowledge except watching a You Tube video would not have attempted mixing it with another chemical solution, who knows what the result could have been.

Last edited by John King; 23rd January 2022 at 07:51 AM.
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Old 23rd January 2022, 11:41 AM
Lostlabours Lostlabours is offline
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Greg Davis is very precise in his explanations and workings, technically excellent. However, he isn't saying what paper and chemistry he's using, and that may mean the techniques don't work with all materials.

Kodak did use similar (unpublished) contrast control techniques when they introduced their early neg/positive papers, this was how they controlled the consistency of the contrast of different Ernst Haas prints.

Other techniques have been used, the Colour prints are exposed as normal, then developed in a B&W print developer, stop bath,B&W fix, wash, bleach in a rehalogenating Ferricyanide/Bromide bleach, wash again, re-expose to bright light, then RA-4 process as normal. The choice of the B&W developer controls the contrast, ID-3/D165 to lower contrast and Dektol/D72 for increased contrast.

Ian

Last edited by Lostlabours; 23rd January 2022 at 12:00 PM.
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Old 23rd January 2022, 12:14 PM
John King John King is offline
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Irrespective of the concentration they were using, Hydrogen Peroxide is hazardous and I would suggest not suitable for use in a darkroom.

The real answer is get the exposure/development right in the 1st place.
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Old 23rd January 2022, 02:44 PM
Lostlabours Lostlabours is offline
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The RA-4 developer is far more dangerous than the weak 3% Hydrogen Peroxide that Greg Davis suggests in his video. It's in fact medical grade and can be used on the skin, or diluted 1+1 with water as a mouth wash. 12% Hydrogen Peroxide is sold as Food Grade.

So, one of the least dangerous chemicals you could use in a darkroom. It's used in two formulae I mix occasionally for the Etch Bleach process, both Ilford & Kentmere published data sheets for the process.

There has to be a reality about chemical safety, proper storage and clean working. But it's often forgotten how dangerous/hazardous some household chemicals are. Having run an analysis lab I had to draw up a COHS Lab Safety report, this included all chemistry we used, working methods, storage, and equipment used and regularity of safety checks.

As a result of this I realised that most darkroom tray warmers aren't particularly safe and I use a circuit breaker.

Ian
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Old 23rd January 2022, 04:49 PM
MikeHeller MikeHeller is offline
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Quote:
Originally Posted by Lostlabours View Post
As a result of this I realised that most darkroom tray warmers aren't particularly safe and I use a circuit breaker.

Ian
I have experienced this when a Nova heating mat burnt a hole into the work surface formica covering. Nova made me an offer of a discount for a vertical processor (toaster) which I eagerly accepted and is still in use.

Mike
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Old 26th January 2022, 04:25 PM
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Bob Bob is offline
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Quote:
Originally Posted by Lostlabours View Post
<snip>
As a result of this I realised that most darkroom tray warmers aren't particularly safe and I use a circuit breaker.

Ian
Just a note to reinforce this suggestion to all. If your home does not have an RCD (residual current device) in your consumer unit ("fuse box" for us old-timers...) invest in a plug-in RCD adaptor for anything close to water in the darkroom to protect you from an electrical fault. We can spend a lot of time in the darkroom on our own...
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