Big demand at Sotheby’s, Christies and other art auction houses for verification of antiquity claim. Mostly Chinese and Italian renaissance porcelain. Samples are taken by small drill technique; ~100mg are necessary for TL test.
The base and the underside of the horse are made from genuine pieces of porcelain from the period, but the saddle, neck and tail are more recent.
Forger’s learn physics
40 per cent of objects tested by the Thermoluminescence Laboratories are proven to be fakes; half the antiquities brought for sale at Sotheby’s are fake; 5,000 forgeries of ancient art enter the market each year. To overcome the handicap of TL dating forgers expose sample to radiation. Difficulty is however the homogeneous distribution of natural radioactivity versus external exposure. Efficient exposure can be done only with γsources, external β exposure would only increase TL from surface material of sample due to the short range of β radiation. TL tests indeed indicate that several fake porcelain pieces have been artificially β radiated to produce TL signature.
What γ dose is necessary for creating a TL signature of a T’ang porcelain horse for a 20 year old forgery?
How Long Does It Take?
The African Ram $275 000 at Sotheby’s
How to Circumvent Thermoluminescence Tests Having partially reconstructed the history of the Kuhn ram — its export to the United States by antiquities dealer Samba Kamissoko and its acquisition by New Orleans dealer Charles Davis, I wanted to learn how Amadou faked objects that deceived experts in African art. Even if Amadou were capable of reproducing the ancient terracotta’s, how was he able to circumvent thermo-luminescence dating tests?
How it is done
In addition to joining larger authentic pieces to fabricated parts, Amadou explained that he digs “holes into the clay where I can bury fragments of authentic terra cotta found at the [looted] sites; I do this after firing the new clay. As far as the piece [the Kuhn ram] you showed me is concerned, I put ancient fragments in the two hind legs and other pieces in the stomach.’ Amadou’s explanation was believable; I had heard about the technique a few years earlier from an Italian restorer, who described it to me as “both risky and infallible –infallible because TL can’t distinguish an inserted part from the rest of the object … and hazardous because it’s necessary that the TL technician choose to test in an area where authentic pieces were inserted.”
I was interested to find out if this method worked, so I traveled to Daybreak Nuclear and Medical Systems, Inc., the Guilford, Connecticut, TL lab that had tested the Kuhn Ram. I hoped I’d be able to see the test results. After a good amount of hesitation (client documents are generally confidential), Victor Bortolot, the lab’s’ director, agreed to search his archives for dossier 2OIA36. Judging the object to be authentic, the technician at the time had taken only a single sample, from under the left front leg, an authentic part of the piece. Hence the favorable test results published in the Sotheby’s catalog, hence the high price fetched by the piece. “But don’t forget that this file dates to March 1988,” Bortolot said.’At the time our practice was to make only one test if we felt the object was good. But now, with the great number of fakes circulating, it’s necessary to make at least two.”