Every month at the Museum of Liverpool a hundred of so finds come in to be recorded on the database. Many of these finds have been recovered from the plough soil in the previous months and are well looked after by their finders. However there are always one or two which arrive ‘treated’ with olive oil!
The first indication of this ‘treatment’ is usually the smell which blasts out of the finds bag upon opening. The ‘treated’ finds appear darker in colour, which some find aesthetically pleasing, but which changes the patina and for finds which are difficult to date, due to being in use throughout several periods, this obscuring of the natural patina makes dating the object considerably more difficult. But apart from my dislike of the smell and the difficulties dating some objects there is a more serious reason why you should put the olive oil down!
Here is the science bit!
Conservator Pieta Greaves of drakonheritage.co.uk explains: The main problem with olive oil is that it is a fat, it is effected by oxygen and light so degrades quickly if just left around. Essentially people are exposing objects to something that begins to rot and goes rancid inside the object. It also is likely to contain sulphur which actively attacks metals in particular. It is not reversible as a treatment and will in the end destroy the object.
Some oils can be good for wood/leather; I assume that this is why people think they can use it on anything. Historically oils were used on objects; these objects are no longer around anymore or are in very little pieces.
If you are worried about the condition of your objects please follow the advice provided in the PAS Conservation Advice notes handbook or contact a conservator and leave the olive oil in the kitchen where it belongs!