Gelatin preservatives

[Photo Engineer]

I have been asked what the options are for various gelatin preservatives.

Here is a list in ascending order of potency. Thymol, Thujaplicin, Phenol, Ottasept and Kathon.

Thymol we all know about, Thujaplicin was once used by Kodak and Phenol is currently in use by several companies including Ilford. Thujaplicin is very expensive, and at least 2x better than Thymol. Phenol is very good but very very toxic and causes severe, often permanent damage to humans in the form of burns and nerve destruction. DO NOT USE IT. Just posted FYI. Ottacept, (4-chloro, 3, 4 dimethyl phenol is the active ingredient) is quite good, about 40x better than Thymol, and presents low risk to humans if proper precautions are taken such as rubber gloves and a good lab coat.

Kathon is a recent addition to the Kodak repertoire and is superb, but very very toxic to fish and requires a special license for use in most locations. It is used in some color photographic stabilizers (final rinses) and this presents the possible use for a final rinse being used as both a preservative and surfactant in emulsions.

I suggest you stick with Thymol unless you need a really strong preservative. In that case, use the Ottacept active ingredient but use it with caution. It extreme cases, try a color final rinse.

In all cases, these ingredients, being organic, alter the spread characteristics of an emulsion on paper, film and glass.

Have fun - safely.

PE

 

[MattKing]

Thymol is a restricted product in Canada - you normally cannot obtain it legally unless you are a commercial beekeeper.
I have no idea why.

 

[Andrew O'Neill]

Luckily I've never needed a preservative, as I use up my gelatine mixtures soon after mixing.

 

[Photo Engineer]

Thymol is a restricted product in Canada - you normally cannot obtain it legally unless you are a commercial beekeeper.
I have no idea why.

Use Listerine then. The active ingredient in it is Thymol. I have never tested this bizarre suggestion though. Just OTOMH.

PE

 

[1kgcoffee]

Never tried anything like this, but I'm curious if something like eugenol (ie clove oil) would also work? The molecules look pretty similar but I'm no chemist..

 

[MattKing]

Use Listerine then. The active ingredient in it is Thymol.

Only the original version though. The other, more common modern versions don't have it.

 

[Nodda Duma]

Any feel for how long / under what storage conditions the different preservatives keep the emulsion happy and free of illness?

 

[RauschenOderKorn]

Use Listerine then. The active ingredient in it is Thymol. I have never tested this bizarre suggestion though. Just OTOMH.

PE

I have tested it as a preservative for 1,5% citric acid stop bath, at a rate of 10-20 ml / l.
Works like a charm, the stop bath did not go bad before being exhausted (instead of in 1 week max.) and left not stains / marks / strange things on films or prints.

 

[Photo Engineer]

I have a modern bottle of Listerine. It still lists Thymol on the label. Perhaps this change is only true in Canada?

As for keeping, all I can rely on is the estimates of Ottacept being up to 40x better preserving gelatin than Thymol, when kept in a refrigerator. I've been told that Kathon is so good you literally don't have to refrigerate gelatin. Of course, I would not want to do that.

I have never tested these in rigorous experiments myself. I am relying on what I have been told by others. I know that all of the cold storage lockers at EK smelled strongly of Ottacept and that one year was the max keeping allowed for a gelatin preparation.

PE