View Full Version : Substituting chrome alum with glyoxal

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12-13-2011, 09:35 AM
Many of the older emulsion formulas in Wall's and Eder's require chrome alum with is nearly impossible to get as an individual in Austria, therefore my question can chrome alum be substituted with glyoxal or other easier obtainable hardeners?

Thanks Dominik

12-13-2011, 10:48 AM

In my experience/opinion, it depends on whether you are coating film, glass, or paper. Glyoxal is far better for paper, but it's a disaster with glass, unless your goal is emulsion transfer! Hardeners of any kind are by and large unnecessary for glass (if processing solutions and washing water temps are kept between 65F and 68F and all the same temperature, and you handle the plates with reasonable care.) I'm still deciding on film. Right now, I'm using a hardening stop bath (made with chrome alum) and hardening fixer. This is on 3M subbed film. I haven't noticed a problem on Dupont (Melinex) film or hand-subbed acetate, so...jury still out. I have been meaning to try grocery store canning alum in a stop bath, just to know. Is that available to you?


12-13-2011, 12:20 PM
Thank you Denise. Is pickling/canning alum potassium alum if so I still have plenty of it?


12-13-2011, 02:20 PM
Yes. Sorry to not specify that.

Here's what Wall said in the 1912 Dictionary of Photography: "Chrome Alum...soluble 1 part in 10 cold water...It is used for hardening gelatine, as, for example, in the preparation of emulsions for dry plates to prevent frilling... Potash Alum..It is used for rendering the films of gelatine less liable to mechanical injury, by hardening them, and also clears them from stains. Solubility: 9.5 in 100 of cold water, 10 in 8 of boiling water..."

I take this to mean that chrome alum was traditionally used as a final addition to the emulsion itself, and that potassium alum was used in hardening baths. If so, it still needs some investigation to see if that would work for us. "Alum" just went on my grocery list. I've never used chrome alum in any of my emulsions, so the issue about its availability has slipped under my radar. Thanks for bringing this up :).

Gerald C Koch
12-13-2011, 02:37 PM
Potash alum (potassium aluminum sulfate) is not as good a hardener as chrome alum (potassium chromium sulfate). Years ago when elumlsions were softer then they are now I regularly used a 3% solution of chrome alum as a stop bath when processing film.

12-13-2011, 03:25 PM
Please note that "grocery store" alum is likely to contain flow/anti-clumping agents which make it a no-no for emulsion work. As a hardening bath during processing, K alum works reasonably well, if given a bit of help with a strong acid.

Glutaraldehyde is a reasonable hardener for paper emulsions, but it is rather fast and touchy - turn your back on it and you might find your emulsion has turned into rubber :( btdt

12-13-2011, 03:56 PM
Can't you do a little write-up on the differences between the 3M and Dupont substrates, Denise? Pro and cons, anything to be aware of, that sort of stuff.

12-13-2011, 06:50 PM
Jerevan, I'm still working through the two films. They're almost identical and I couldn't swear that any differences I think I see are inherent to the material or a fallout of my imperfect duplication of conditions. The big thing is that 3M sells retail, both 6.8 mil (sheet film thickness) and 3.9 mil (roll film) Right now, I think that the 3M film may not have the adhesion that the Dupont material does, but that the Dupont film has a greater tendency to make comets (repellency spots.) Again, though, could be my imagination, or there could be something significant I haven't run across yet. You know me, when I find out more, I'll blog my heart out. I do know that both are great to work with. Love 'em.

Ian, I totally agree about grocery store chemicals in the emulsion itself. Given that all the other ingredients together don't touch the cost of silver nitrate, why bother? Having said that, I do have a paper recipe I love that uses sea salt. Goes to show -- no hard and fast rules. Where I think that grocery store chemicals have a real place is in the processing chemistry. Chances are that even if some of the necessary emulsion chemicals get restricted or expensive, it will always be possible to get (and afford) small amounts from lab supply companies. The quantities used in emulsions are so tiny that even an expensive chemical wouldn't cost much in the long run. But, the quantities used in development is a different story. Food grade potassium alum is quite pure. It would be fine in hardening baths. One additional nice thing about the diy/grocery store processing chemistry: likely less environmental fallout. I love the idea of Caffenol, etc.

01-07-2012, 07:08 AM
What about canvas coating? Can you substitute chrome alum not with glyoxal, but with glyoxal trimer dihydrate (CAS 4405-13-4)? I'm asking since, similarly to Austria, chrome alum is rather hard to get in Croatia and the aforementioned dihydrate is the only form of proper hardener made over here.

Kirk Keyes
01-07-2012, 03:25 PM
My understanding is that chromium which reacts with gelatin when used as a hardener has an affinity towards the silica in glass and it is able to help the gelatin bind to a glass substrate.

01-08-2012, 10:54 AM
Personaly, between chrome alum , Glyoxal and Formalin, I have never observed an advantage in chrome alum over the other two hardeners. Glass plates are the only kinde of emulsions I make. Glass cleaning is vastly more important than glass adhesion promoters. While it is true that my emulsions contain silane, If I don't clean my glass to the standard of a "standing sheet" of water, I WILL see frilling and cratering. Please see my glass cleaning proceedure on www.thelightfarm.com and www. alternativephotography.com. Also, one must be very careful of the type and amount of surfactant one uses when the substrate is glass. The wrong kind, or too much surfactant can realy destroy adhesion to glass. I like Triton X200, in tiny amounts.

Photo Engineer
01-08-2012, 11:06 AM
Use chrome alum in emulsions for glass coatings. For film coatings use an aldehyde hardener or use chrome alum but with a longer drying time before use. Chrome alum is slower to harden. The old writers note that emulsions can be stored in the cold with chrome alum for quite some time.

Use of Chrome Alum or Glyoxal are best done at the same quantity per unit of gelatin and so I use 10% Chrome alum or I dilute commercial 40% Glyoxal to 4% (I call it 10% Glyoxal) and use either at the rate of 5 ml / 120 grams of 10% gelatin. The Glyoxal will harden in 4 - 8 hours, but the Chrome Alum requires about 24 - 36 hours.


01-08-2012, 11:49 AM
PE, is there a significant difference between glyoxal and glyoxal trimer dihydrate (CAS 4405-13-4) that makes the latter unfit for adding to emulsion? The acrylic-primed canvas has been prepared with the mixture of gelatin and isopropyl alcohol.

Photo Engineer
01-08-2012, 01:45 PM
Glyoxal trimer is probably similar to the Formaldehyde trimer that forms from Formaldehyde. I have never worked with the trimer, but I can tell you that it must be hydrolyzed to the monomer before it can work properly. The Formaldehyde trimer works but much more slowly than Formaldehyde itself.

That is about all I can tell you, never having worked with it before.


01-08-2012, 02:19 PM
Regarding the trimer of Glyoxal:

The trimer when dissolved to produce a weak solution will revert to the monomer within 24 hours (in darkness).. so claims a paper on the fixation of tissue samples. Unfortunately, it doesn't supply quantities, but does reference a another paper - Earl B. Whipple, "The Structure of Glyoxal in Water" (http://pubs.acs.org/doi/abs/10.1021/ja00727a027). So far I haven't been able to find a free copy of Whipple's paper - JACS wants $$ to read :(

Photo Engineer
01-08-2012, 03:07 PM
Then I would use the trimer mole for mole re glyoxal and wait 24 hours before using it.


01-11-2012, 04:07 AM
Hexavalent and PE, thank you for the info. I will then try dissolving the glyoxal trimer in water. Should I use distilled water? What might be the trimer : water ratio?

Kirk Keyes
01-11-2012, 08:30 AM
Trimer = polymer consisting of 3 identical subunits/precursors.

So the ratio would be 3 water to 1 trimer. But I suspect you want to use a bit more water than that...

Photo Engineer
01-11-2012, 10:07 AM
To allow this to form Glyoxal, I would use 40 grams of trimer and 60 grams of DW to make a standard 40% wt/wt solution. Then I would let that stand for about 2 days and then I would dilute it to working strength by taking 10 g of the Glyoxal and adding 90 grams of water to make a (10%) 4% wt/wt working solution. I would refrigerate everything after this and only take the working solution out as needed.


02-18-2014, 07:17 PM
Hi there,
I mixed the silver bromide emulsion in 125 ml. Can someone tell me how many grams of chrome alum I should add in?