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Marco B
07-09-2008, 07:01 AM
Hi,

I have used Rollei Black Magic VC liquid emulsion several time now and used it in combination with the Rollei RBM glutaralaldehyd based hardener. Using the hardener helped in making the emulsion more robust for wet-processing, as I had some issues with lift-of of the emulsion the first times I tried without hardener.

Now I have just one simple question: What's the shelf life of hardener? Do they oxidise like for example a developer? I ask this because, contrary to most other chemicals used in photographic processing, where it is quite obvious if and when the solution is exhausted or gone bad, this isn't as obvious with a hardener. You can't see it based on colour or a direct assessment of activity.

So, if for example I keep a half emptied bottle of hardener concentrate for 1 year on the shelf, can I still assume it's good (I had a bottle for about 6 months like that, the hardener still seemed to work). And what about diluted working solution (RBM needs to be diluted 1:20 to get at a working solution that may be added to the emulsion)

Photo Engineer
07-09-2008, 01:39 PM
The hardeners may contain stabilizers, IDK, but they do go bad and should be refrigerated. Many of them polymerize and if they don't they oxidize. Therefore, formalin gives you formic acid, glyoxal gives you a mix of polymers and oxalic acid, and etc.

Please be careful of the glutaraldehyde. It has a relatively high vapor pressure as you might note from the sharp odor, so working in the darkroom with it can be hard on the hands and lungs. Kodak discontinued use of glutaraldehyde and succinaldehyde in E4 and in Xomat processing due to health complaints. There is an existing lawsuit in Australia over this.

Handle with rubber gloves and limit inhalation of fumes as much as possible to the concentrate and to drying prints just after coating.

PE

Marco B
07-09-2008, 02:52 PM
Thanks for the detailed info as usual PE! Actually, I haven't noticed a sharp odour coming of the concentrate, I don't know it's exact composition, but it does say that it is a low pH (pH 3) concentrate. Maybe it's buffered at such high pH so as to limit vapour?

I haven't noticed any signs of polymerization, but obviously, I don't know what may have precipitated at the bottom of the bottle.

A few more questions that I hope you can answer based on your info:

- Thanks for warnings about health, I already noticed all warnings about skin, lung and eye damage. I'll try to be even more careful. Will Nitrile gloves be sufficient protection?
- Except for unspecified "damage" to skin, lungs and eyes, what is actually the nature of the thread with this stuff? Chemical burn due to it's acidity and chemical reactivity, or is it also carcinogenic?
- Are there any less harmful hardeners, what do you recommend and where do I buy them?
- Just some wild thought, but I have been wondering: can I actually "overdose" a hardener? Will it damage paper in the long run or be a thread to print longevity? Or is this just all nonsense? (well, probably, any left over hardener is simply washed out during development and subsequent washing)

Photo Engineer
07-09-2008, 03:51 PM
In order, nitrile gloves should help.

Skin is gelatin, and the soft wet tissue of the lungs easily crosslink with inhaled hardeners, hardening the lungs and causing what amounts to the onset of emphysema or chronic bronchitis. Some are suspected carcinogens.

Glyoxal is apparently less harmful. It is readily available. It comes as a 40% solution in water which you take 10 parts of and dilute to 100 ml. Use this at 5ml / 200 ml of 10% gelatin for hardening within about 8 hours.

An overdose of hardener put into your emulsion can lead to a coating that is too soft. You have to have not more than 50% of the amount of hardener than can react fully with gelatin. If you go over that amount, it does not harden. Hardener is not washed out unless you process too soon, but in that case the emulsion will probably wash off as well.

Last but not least, the pH 3 concentrate is probably stabilzed by the pH and therefore would lose its stability only when diluted.

PE

Marco B
07-09-2008, 04:04 PM
Thanks for your excellent answers! Much help. I will look into Glyoxal when the current stock of RBM5 runs out.