How can the paint itself prove a painting is too young to be real?

The paint can prove a painting is too young because many pigments first appeared at a known date, and a painting cannot contain an ingredient that did not yet exist. If investigators find an element that was not historically used in objects of that type, the object is not authentic. Find a too-modern pigment in a picture that is supposed to be old, and you have caught an anachronism that no story can explain away.

Titanium white is the classic example. Until well into the nineteenth century, lead white was the sole white pigment used in European easel painting. Titanium dioxide, a bright white substance, was first created in a laboratory in the mid-19th century, developed as an industrial pigment in the 1910s, and by the late 1920s titanium and zinc white had unseated lead white as the dominant white on the market.

That date helped to unmask the forger Wolfgang Beltracchi. He sold a fake Campendonk, Red Picture with Horses, as a painting of 1914. It had been made with a Dutch paint tube, and a 2008 analysis showed it contained titanium white, which was not yet available in 1914. Beltracchi remembered that the forgery was uncovered because, this one time, he had not mixed his own paint.

The test only works in one direction. A too-modern ingredient proves a work is not authentic, but an old-fashioned one proves nothing, because a careful forger can use period materials.