Sunday 30 September 2012

Metal Detecting Under the Microscope: "Preserving" finds in Olive Oil - Don't


A metal detectorist in a comment to an earlier blog post of mine this afternoon admits that the dark gundgy appearance of the artefacts in his videos was due to his use of OLIVE OIL to "preserve" the corroded metal. Now I think we are all aware of the use of olive oil to preserve herbs, cheese, olives, pickled garlic and other foodstuffs, but archaeological artefacts? I would have thought it pretty obvious this is no way to treat an ancient artefact of any kind, let alone anything recovered from the soil.

As any health food buff will know (and anybody else can easily find out), olive oil contains a lot of free fatty acids and polyphenols. These are not good things for soaking ancient corroded metal objects in - especially as they themselves can break down in contact with the metal corrosion products.

I am at a loss to think where this idea came from. While it is true that soaking in olive oil ifs one of the methods used to strip thick corrosion from cruddy coins by so-called "coin zappers", that term alone should give an indication of the relationship of the techniques used by these people in relation to real archaeological conservation. As I said, it is a method used by them (alongside other even more chemically violent methods)  to strip corroded metal out, not preserve it. One metal detecting site gives an "Introduction to Coin Cleaning (advanced)"
There are many recommendations for coin cleaning that entail soaking in oil. This is risky business, and may introduce chemicals to the metal that are not good for it. Soaking in oil will not accomplish anything that soaking in water does not, and it adds the problem of removing the oil if that becomes necessary during further steps of restoration. Oils can sometimes be removed with detergents, but again, that means more chemicals to upset what has become, over 2000 or so years, a rather tenuous chemical balance. It is our suggestion that water be used in lieu of oil, and that you preclude all use of any oils in treating your coins except perhaps for some very esoteric circumstances during the finishing process. Olive oil in particular is extremely acidic, and etches ancient bronze destructively.
The Portable Antiquities Scheme has Conservation advice for finders, part 5 of which deals with "Cleaning and protecting" (it is actually called "Take Advice Before Cleaning"). This does not advocate the use of olive oil for treating artefacts, indeed it says:
 "Don't use domestic waxes, oils, petroleum jelly or shoe-polish they all contain potentially harmful contaminants"
The problem here is that artefact hunters often have not the training and knowledge to properly curate the elements of the archaeological resource that fall into their hands, and even when such information is made available (in "partnership"), there will always be a whole mass of artefact hunters who are either not going to look for such information, or if they find it will ignore it.

Mr Stavast and your fellow olive-oil-loving detectorists, please stop using olive oil to damage historic finds, use it by all means for soaking your wife's new jewellery, or your car, but not for elements of the common archaeological heritage of which you are but a temporary custodian


DA said...

as a supoosed man of "Science" you should take some advice as well .. Do your home work and talk to people who have worked to develope your so called COIN zAPPErs You are clueless in this arena of study because if you have done 1 minute of research you have LEARNED that electrolytic stabilizing Strips Nothing from an old coin or relic .. It stabilizes metal and is used in your "SUPPOSED " industry ,extensively .
The phenomenon of SO CALLED EXPERTS spouting off ALTERNATE FACTS , about topics the know nothing about is truly getting old ..... Well I can't locate your credentials but Id be happy to give you mine and I'll back up everything I know about coin cleaning with olive oil and electrolysis . Why don't you reveal your scary scientific process .I doubt you will as screwing up 1 attempt at preserving an artifact doesn't make you an expert

Paul Barford said...

"electrolytic stabilizing Strips Nothing from an old coin or relic" well, except the original surface preserved WITHIN the corrosion products. You, sir are the one who is wrong - I assure you. Do your 'credentials' cover sucking eggs as well as the academic study of the complexities of corrosion processes in the soil?

DA said...

The phenomenon of SO CALLED "SCIENTISTS" pouting ALTERNATIVE FACTS is getting old ... Do you really believe the stuff you say or are you just hoping to snag an unsuspecting reader or 2 . OLIVE OIL in artifact cleaning Came from an Ivy league Study and electrolysis strips nothing away from a coin or artifact it simply stabilizes the metal which is in a volatile state ... If you spent 1 minute on your research you would have easily figured that out .. But since you screwed up your 1 attempt using these elements you simply figured everyone else must be screwing it up as well.
30 years of research and study with a IVY LEAGE University 12 museums and 100 archaeo and salvage vessels using this technology say youre wrong ... PLEASE I'm intrigued , I would love to know what Scary scientific method you used to develop your theory ... Id be More than happy to present mine . The targets of your very slighted info have been used in your alleged arena of study for many years ... and some of the most well preserved artifacts in the world are in that state because of electrolysis ...a 5000 year old process developed by primitives who apparently have more of a grasp of the scientific method than you sir

DA said...

As an expert you are obviously talking patina . patina is NOT and original element.. it is a by product of metallurgic deterioration ...leach and oxidation of elements ... coins not in need of stabilizing don't need electrolysis artifacts not in need of stabilizing do not need electrolysis ... but your tooth pick method will not stabilize metals reaching critical mass and passing the point of NO return .... Theres a reason Museums and colleges reach out to us and there's a reason they quickly dismiss your weak theories

Paul Barford said...

Oh my, do they require one to be able to read and write articulately in those 'Ivy League' places you are so proud of? 'No kid left behind', innit? Except the ones that are. I think if you'd read the post to which this is a comment, you'd realise that it is not I who have tried olive oil and failed.

Mr "DA", whoever you are and however much ivy you have up your walls, nobody is interested in your "qualifications". I have seen what electrolysis does to artefacts and am not a bit interested in your opinion.

Paul Barford said...

Believe me, I do not take a toothpick to uranium artefacts reaching 'critical mass' but I think you are referring to chlorides... This is what electrolysis does to artefacts.

The Girl With No Regrets said...

Thank you for this. I'm a conservator and am currently treating two objects that were coated in olive oil - one of them is a bronze age axe head and the oil has destroyed the surface causing a lot of damage. The other is a Roman knife handle which so far doesn't look too badly damaged but until I start the actual treatment I won't actually know.

Unknown said...

So what can the ordinary layman detectorist do to enchance his ancient artifacts without harming them, ie is there something I can easily lay my hands on please.

Paul Barford said...

What do you mean by "enhance"? We have these things called "books" and maybe the answer you need is there, don't you think? Most collectors fail to heed the advice "before you get the coin, read the book". May metal detectorists try to do it the other way round.

I am told they "study" their artefacts, you'd probably do that easier if they were not all slimy and shiny by smearing oil over them (the oil gets on the pages of the book as you read up on them, and the keys of the computer when you write about them).

Paul Barford said...

Once again, this is what the Portable Antiquities Scheme has published for "finders (and keepers):

It's not exhaustive, but a good start.

Creative Commons License
Ten utwór jest dostępny na licencji Creative Commons Uznanie autorstwa-Bez utworów zależnych 3.0 Unported.