Radioactive decay
Forgeries in which modern lead or white lead pigment has been used can be recognized by using a technique called Pb(Lead)-210-Dating. Pb-210 is a naturally occurring radioactive isotope of lead that is part of the uranium-238 Radioactive decay series, and has a half-life of 22.3 years. To determine the amount of Pb-210, the alpha radiation emitted by another element, polonium-210 (Po-210), is measured. Thus it is possible to estimate the age of a painting, within a few years' span, by extrapolating the Pb-210 content present in the paint used to create the painting.