Avoiding potassium dichromate in bromoil process

[removed account4]

thanks ned !! i appreciate the moved link
and your clear-headed reasonings.

 

[pramil]

Hi Everybody,

Just re-activating this topic (has potassium dichromate have recently been banned in Europe) : I'm looking for an alternative to potassium dichromate in the bleaching step of bromoils print.
The idea of introducing a tanning agent in the development process look's interesting. Did anyone suceeded in this task ?

I've heard Diazidostilbene or ferric ammonium citrate are being used has an alternate in some processes (Chiba system for exemple), but they need UV + hydrogen peroxyde to fully polymerize the gelatin.. these agents are probably useable but in oleotypes but not in bromoils has long has we use "industrial-made" chlorobromide papers (FOMA - Fomabrom 112 MAT for ex.).

if anyone finds the solution, I'll be happy if he/she could share..

Thanks in advance,

Pramil

 

[Gerald C Koch]

If one wishes to work with Daguerrotypes or bromoil prints you have to use toxic substances. In the case of bromoil only dichromate will provide the amount of hardening necessary. The gelatine substrate takes quit a beating in the the process.Things like tanning developers, other hardening agents like glutaraldehyde, will not work.

 

[pramil]

Thanks for you reply,

Seems that it's the end of this practice (Bromoil), for the good (some would say).
However, I guess that we still can acheive "oil printing" using a homemade gelatin paper with ferric ammonium citrate as the sensitizer + peroxyde hydrogen for polymerizing the gelatin.

Did someone tried this technique already ?

Best regards,

Pramil

 

[Wayne]

Hi Everybody,

Just re-activating this topic (has potassium dichromate have recently been banned in Europe) : I'm looking for an alternative to potassium dichromate in the bleaching step of bromoils print.
The idea of introducing a tanning agent in the development process look's interesting. Did anyone suceeded in this task ?

I've heard Diazidostilbene or ferric ammonium citrate are being used has an alternate in some processes (Chiba system for exemple), but they need UV + hydrogen peroxyde to fully polymerize the gelatin.. these agents are probably useable but in oleotypes but not in bromoils has long has we use "industrial-made" chlorobromide papers (FOMA - Fomabrom 112 MAT for ex.).

if anyone finds the solution, I'll be happy if he/she could share..

Thanks in advance,

Pramil

I have only gotten back into the darkroom this week for the 2nd or 3rd tme since last February. I hope to experiment some more with that hardening developer idea this winter (which probably won't work) but for the immediate future all I see is RA4. The farthest I got was what I quoted above in #43. The basic hydroquinone developer idea worked well enough to develop prints, but I have no idea how much it hardened.

 

[Vaughn]

How about diazidostilbene (DAS)? It has been/is being used in color carbon printing instead of the dichromates...currently undergoing testing by Sandy King for monocromatic single transfer carbon. printing.

 

[Wayne]

How about diazidostilbene (DAS)? It has been/is being used in color carbon printing instead of the dichromates...currently undergoing testing by Sandy King for monocromatic single transfer carbon. printing.

Looks like it will stain https://www.photrio.com/forum/threads/bromoil-and-dichromate-replacement.146602/

 

[Vaughn]

I think Sandy is finding that it does not at low concentrations...I'll see what I can come up with.

 

[Jerevan]

Hi Everybody,

Just re-activating this topic (has potassium dichromate have recently been banned in Europe)

So, tell me - where is the source of this "ban"? For non-commercial (private) use or overall commercially? The dichromates have been in the spotlight for decades, with pointers to the obvious heath risks.

 

[Wayne]

So, tell me - where is the source of this "ban"?

Potassium dichromate, included in Annex XIV of the REACH Regulation, will be completely banned in Europe from 21 September 2017.
https://www.ecomundo.eu/en/blog/eur...horisation-for-2-uses of-potassium-dichromate

 

[Wayne]

I think Sandy is finding that it does not at low concentrations...I'll see what I can come up with.

Did you come up with anything?

 

[Vaughn]

No -- I have been without internet for a little over a month -- not a bad thing as I was in Zion National Park on an Artist-in-residence and just got back today. Try contacting Sandy King directly.

sanking@clemson.edu

 

[Wayne]

No -- I have been without internet for a little over a month -- not a bad thing as I was in Zion National Park on an Artist-in-residence and just got back today. Try contacting Sandy King directly.

sanking@clemson.edu

Then I have to do the work, and I dont have time for it. That's why I thought it was nice that you volunteered.

 

[Raghu Kuvempunagar]

There are two requirements for making a compound work for this process:

1. The compound has to tan gelatin
2. It must do this only in the presence of developed silver or developable silver halide, not everywhere

Hi Rudy,

Regarding point #2 above, I didn't quite understand how a dichromate bleach would tan gelatin in the presence of developable silver halide. Can you please explain? Thanks in advance.

 

[Nikola Dulgiarov]

Hi Rudy,

Regarding point #2 above, I didn't quite understand how a dichromate bleach would tan gelatin in the presence of developable silver halide. Can you please explain? Thanks in advance.

I believe Rudi was generalizing about the class of agents that would work in this application. Dichromate's tanning action is "stoichiometric" vis the available metallic silver in the gelatin, AFAIK. That is, for Cr2O7 to tan gelatin, it must oxidize the respective amount of silver present. This is opposite to the tanning developer agents, which need to become oxidised while reducing a developable silver halide in order to have a hardening effect.

One could theorize that an agent exists, which can harden gelatin based only on exposed silver halide, either without developing it, or by both developing and eliminating (bleaching) it simultaneously. But I have not encountered such a chemical in the literature (or in real life )

 

[Raghu Kuvempunagar]

I believe Rudi was generalizing about the class of agents that would work in this application. Dichromate's tanning action is "stoichiometric" vis the available metallic silver in the gelatin, AFAIK. That is, for Cr2O7 to tan gelatin, it must oxidize the respective amount of silver present.

Ok, now it makes sense. Thanks @Nikola Dulgiarov.