John is about to enter another minefield. I know a detectorist who regularly ‘cleans’ his coins in a barrelling machine. Every coin. Luckily, he hasn’t yet unearthed a historically important item. He prefers that his finds be abraded in this way. Afterwards he smears them liberally in some sort of ‘preserving’ gunk leaving them with a strange green-like glistening hue. I’m not sure that he knows, but he is universally referred amongst his friends as Mr. Shiny. Our friend is revered on detecting forums because the knowledge he has gleaned over many years of metal detecting is second to none. Just, don’t seek his advice on cleaning.
I’m reminded of something detectorist Neil Allen said in a conservation group meeting at the British Museum, whose proceedings, Whose Find is it Anyway? was published in 2006. He said:
“In the past, conservators were aloof … so this left the market open for publications by enthusiastic amateurs. Unfortunately, some of their advice was not of a high standard … these publications gave instructions on how to use a barrelling machine. It comes in three sizes: destruction, total destruction and universal Armageddon – and you can turn destruction into universal Armageddon by leaving it on longer!
They went on to show how to burn away patina my using acids and then had to repatinate using flowers of sulphur and petroleum jelly. Good stuff isn’t it? You could clean silver coins using washing soda, aluminium foil and boiling water. Excellence for your choice and medieval finds. It went on to explain that you should coat your find with olive oil and shine up the remaining gold gilding with lemon juice.
Olive oil and lemon juice – it doesn’t sound like conservation … it sounds like the beginning of a Jamie Oliver salad dressing. Another idea was bead-blasting iron objects I won’t go on … it’s too horrible.” Neil Allen
Your Starter Cleaning Kit
I don’t know where I first read it, but there’s a great piece of advice in a saying that tells us that cleaning coins is like marriage and shouldn’t be embarked on lightly. Or have I just made that up? Translated, that simply means DON’T DO IT! It’s far better to have a dirty coin with it’s original patina, than have one that is irretrievably damaged.
Conservation Advice from the PAS
As a rule of thumb, the older the item, the more heavily corroded it will be, and many ancient objects made from copper alloy will have developed a patina which adds value and beauty to the object. Removing this patina could seriously damage and devalue the object and destroy information. But many of your finds will be fairly modern, like milled coinage, watch-fobs, penknives and other casual losses. These more recent items can mostly be cleaned carefully without them coming to harm but there are no ‘quick fixes’!