One magicians take...
“The Museé Terrus in Elne, France, saw its collection cut by more than half when it was revealed that 82 of the museum's 142 works were forgeries,” according to National Geographic.
For what ever reason – and I think you know – this fascinates me. There are people out there with extraordinary artistic ability to paint, but paint only paintings that they sign with another person's name. (We'll leave this foray into the world of art forgery as only those done with paint.)
The museum cited above must have really been hurt by this. From what I understand, It's easier to forge the work of a lesser known artist. Forging Picasso, or Renoir you need to fool some of the most ardent art scholars. It can be done, and sometimes is, even today, but it's much easier to forge a Terrus.
When you forge a Picasso, every one is watching. When you forge a Terrus, no one is really paying attention. In fact, the person doing acquisition for the museum was the founder, a kind of part time curator. Sadly, he's receives no training.
From same article,“A fake is a pre-existing work of art that has been altered in some way to fraudulently increase its value,” says Charney. “A forgery is a new work created wholesale from scratch in fraudulent imitation of something else or the style of another artist.”
In magic there is something similar to a fake known as a feint. A move that is designed to look like another move, but the first few times, nothing happens. When you are used to it, that's when the dirty work happens.
A painting looks enough like the other paintings by that artist, and you believe that what you're seeing is the real thing.
In an effort to fight fakes and forgeries, Sotheby's recently acquired a forensic lab to vet art. You can be sure the Museé Terrus probably can't afford that.