Saturday, January 25, 2014


Museums clean ancient coins before putting them on display. Dealers and collectors often clean coins and many have their own favorite 'recipes' for cleaning.

A much bigger problem is the cleaning of paper money. The researchers Nabil Lawandy and Andrei Smuk claim that 150,000 tons worth of paper money, unfit for recirculation, are removed from circulation every year at a cost of $10,000,000,000. The researchers have developed a method using supercritical CO2 at 60°C and 5000 psi said to effectively clean both paper and polymer banknotes.

The researcher's paper is entitled Supercritical Fluid Cleaning of Banknotes.

(Hat tip: Marginal Revolution).

I don't collect paper money. Do collectors typically clean it? I have seen a YouTube video (from Suriname the former Dutch Guiana!) showing obsolete banknotes being cleaned in a bucket. Three minutes in the presenter admits he's never done it before!


Paul Barford said...

The video would have benefitted from a bit of editing I feel. It looks a risky process. I've heard of dry processes - one involving fresh bread.

I think it should be stressed that when using commercial cleaning agents (if you must) it would be good to rinse all traces out afterwards, he just rinsed them briefly. I'd say for the long-term preservation, the rinsing out of what he put in should take as long as the cleaning itself.

But then, is not the dirt part of the history of the object, like the patina of a coin?

Ed Snible said...

Paul, I believe there are some postage stamps that are worth more cancelled than fresh because they were created by regimes that fell immediately upon issue and almost never encountered issued.

For modern world coins I prefer an "almost uncirculated" grade that circulated in the country than shiny made-for-collectors proof commemoratives of types that never circulated.

With my collection I try to go for a mix, a combination of "wow I that coin looks new how can it be ancient" and beat-up near-slugs that seem to say something about ancient usage.