A Cure for Old Age! - (for collodion at least).

Collodion doesn't have a great shelf life. Even if kept in the fridge it deteriorates over time.  As the solution ages, it darkens in the bottle from a light straw colour to a deeper orange, almost red.  Old 'red' collodion can still be useable but the sensitivity is generally much reduced and the contrast is higher.  Some people use it to their advantage, using red collodion when they need more contrast or mix it with fresher solution for a custom coating but most of us accept that like conventional photo chemicals it is best to use the stuff up before it goes 'off'.

Recently however I've come across a couple of references to the use of acetone to resurrect old collodion. Quinn Jacobson mentions it and there's a great account on the Collodion User's forum by Tara Oliphant (www.derivedlogic.com)  which recommends using 0.5ml of acetone per 75ml of collodion to restore it. This works out as 6.66ml per litre or 0.0066%. - say .007% for the real world.

As I've got various bottles of elderly stuff lurking in the fridge I tried it. 

The old, red collodion I tested is some of John Brewer's own-recipe positive stuff which must be at least a year if not two years old. (dating the bottles when they are new is a good idea) It's been stored in a fridge at approx. +5deg. C and it still works, though it tends to crack and flake sometimes on larger plates (it's noticeably thicker when pouring).

As per the recipe I added 1.7ml (should be 1.66ml but that's hard to measure accurately!) of acetone to 250ml of collodion. This is a tiny amount: less than 1%of the volume. I doubted anything much would happen but after only an hour the colour had already improved!

After 1 hour the acetone has already lightened the collodion...

Another 9 days in the fridge and it looked almost brand new.  I'd expect the conversion to be quicker if the stuff is left at room temperature but I prefer to keep it safely stored in the airtight fridge.

After 9 days (in the fridge) the treated collodion has reverted to its original colour

Testing.

Side by side tests made under the same lighting conditions - or as best I could in daylight. flash is more consistent but I seldom use it in my wet plate work and I wanted a relevant test result.
For the record these are quarter plates and the lens is my 5" magic lantern petzval.

I established the best exposure for the old red collodion as 6 seconds at f/3.  I kept the exposure the same for the treated collodion (it was a dull day and the light was pretty stable) Here are both plates:

untreated old 'red' collodion. 6 sec f3

same collodion treated with acetone. 6 seconds f3

Interestingly, even though older collodion is supposedly more contrasty the treated stuff has better range. The highlight and shadow are fairly similar (slightly brighter highlights on the acetone one) but the mid tone separation is much improved.
I'm surprised there isn't a greater difference in speed. the light level may have dropped a bit on the second exposure so it's actually brighter than it appears. (another way to test would be to pour both pools of collodion on the same plate so exposure and processing are identical). Anyway, there IS a definite improvement. The 'restored' collodion flows more freely onto the plate - though I think the more obvious crepe lines are a result of inconsistent pouring on my part.
I would expect it to have fewer problems with peeling, though that tends to affect bigger plates so we shall have to see.
(UPDATE:  No, unfortunately  peeling is still a big problem on larger plates. We made this whole plate tintype the other day and it was fine until it came out of the wash and started to dry. The peel started in one corner and spread across the whole image in about 20 minutes. - Heartbreaking!

The general wisdom is to add some alcohol to the collodion - that's IDA (industrial denatured alcohol) for those of us in the UK. - I'll try that next...

At some point I'll try a side by side test of some different collodion recipes as I have a variety in stock. See the excellent wetplatesupplies blog for a very detailed comparison test.