Radiocarbon dating of ancient rock paintings
Before this, the only tool for dating the engravings was stylistic comparison with similar sites on the continent - a far less precise business.
It soon became clear that uranium series techniques could be useful at many other cave art sites.
The process is lengthy and painstaking - researchers must scrape off enough of the calcite crust for an accurate dating, while taking care not to harm the art underneath, or even contaminate the sample with the older limestone behind the art.
Black and violet painted horses overlying red figures at Tito Bustillo, Asturias.
Furthermore, cave paintings are delicate and precious - scraping bits off them to send to the dating lab is rarely welcome.
And there's a serious risk of contaminating the samples being analysed with more modern or older carbon.
For one thing, there's no way of telling whether these materials are contemporary with the art or much older - ancient artists could have drawn with charcoal that was already in the cave when they arrived.
Instead of trying to date the paintings and engravings themselves, they are analysing carbonate deposits like stalactites and stalagmites that have formed over them.