This is the last of my posts on the intensive study of the marbles conducted in early June (at least for now!). In addition to polychromy, we did something that was never before done at the museum (and probably never will be done again): gamma radiography! Two of our marble sculptures (Bacchus and Hercules) posed questions that could only be answered by radiography. We tried x-rays, which we can do in our conservation lab, but these were not strong enough to allow us to see through the marble. We had to go for industrial strength radiography which uses gamma rays. Baker Testing (the company who worked on the Juno at the MFA Boston) did this for us.
Gamma radiography is radioactive, so we had to find a room at the museum that had thick concrete walls and was away from work areas. We did find one, underground, off the art tunnel. We restricted tunnel access to team members and we stayed well clear of the radiography area—all of us geeky enough to know that Bruce Banner turned into the Hulk after being exposed to the rays of a gamma bomb. (None of us wanted to turn green and Kermit the Frog will tell you’ it’s not easy being green!) The radiation zone was actually quite small (we checked with the Geiger counter). The radioactive source was contained in a small Ghostbusters-like unit to which was attached a collimator that focused the beam on the part of the sculpture that needed to be studied. A plate just like those used in x-rays was placed behind the limb to record the information.
We spent the whole day with the guys from Baker Testing, checking the radiographs after they scanned them into their computer, discussing what we were seeing, asking for shots at different angles or more penetration. At the end of the day, Hercules did not turn into Hulk-cules (I have been wanting to say this for weeks!), but while some questions were answered with the gamma, others remain for Mark to puzzle out. The knowledge acquired from those gamma radiographs will help us with the conservation of Bacchus, a major project to be undertaken over the next few years. We could see the rather long metal pins and c-clamps we knew would be holding him together, but we also realized that he suffered a major catastrophic incident that shattered his right side—this resulted in more pins, pegs, clamps, which we could not have seen without the gamma.