The Terrus Museum in southern France recently discovered that 82 of the 140 pieces in its collection are fake.

The authenticity of the paintings in Elne, France – all attributed to the artist tienne Terrus – was brought into question by art historian Eric Forcada, who was guest curating the museum shortly after it acquired about 80 new works.

Forcada’s suspicions were confirmed by a panel of experts commissioned by the town’s mayor, Yves Barniol, according to local TV reports. It had just reopened on Friday after “extensive” renovations with the new additions on display.

“Today, we ask ourselves the question: as art historians, how will we determine fakes in the future?” Forcada said on TV France 3, CNN reported. “This Terrus affair allows us to clean up some of this market.”

The historian noticed that some of the alleged paintings featured buildings in them that weren’t yet constructed when Terrus was alive – from 1857 until his death in 1922. And that his signature was easily wiped off by a gloved hand. Forcada said that paintings by the French artist have sold for upwards of $18,000 and drawings for nearly $2,500.

Terrus was considered a Fauvist-style painter, using bright colors in his impressionist work, perhaps inspired by his friends and fellow famous artists, Andr Derain and Henri Matisse.

An investigation has been launched by local authorities into who is behind the counterfeit art.