In addition to the frieze of 6 bulls (which we are still working on in the Artifact Lab), we are also treating a frieze of 3 birds, in preparation for our new Middle Eastern Galleries, scheduled to open in April 2018.
This is a section of a frieze from the site of Al-Ubaid, Iraq which was excavated by Sir Leonard Woolley in the early 1920s. The birds are the only original pieces of the frieze – the rest is a modern reproduction. The birds (possibly doves?) were carved from limestone and each has a pair of drill holes at their center which would have served as an attachment point. Copper alloy twists would have been used to secure the birds in antiquity – fragments of the original copper remain in one of them.
Due to structural stability issues in the modern reproduction, we needed to disassemble the entire frieze. Once the birds were removed, it was evident that their surfaces were very grimy, related to both the burial environment and time in museum storage. A variety of cleaning methods were explored and tested, but none worked better than using our laser.
The Conservation Department purchased a Compact Phoenix Nd:YAG laser several years ago, and we are still learning about all of its possible applications. We recently had a workshop with conservator and laser-guru Adam Jenkins, which helped us further develop some testing and health and safety protocols.
Essentially, the Nd:YAG laser works like this: the laser emits a beam of light, typically with a wavelength of 1064 nm (in the infrared), which selectively irradiates and removes unwanted dirt and surface coatings without damaging the object (a process called laser ablation). This type of laser cleaning works well for removing dark substances from light-colored objects, so trying it on one of the birds made a lot of sense.
Easy for me to say. I didn’t do this treatment – project conservator Madeleine Neiman did. So she gets all the credit for this.
After testing, Madeleine carried out her first laser cleaning treatment on the bird in the image below. Here she is getting set up to carry out the work:
And here is a shot of the bird after the surface was partially cleaned: (WOW!)
I think the process and results are best displayed in a gif, or a video, so I’m including the gif below, and here is a link to the video.
Go Madeleine! I think this was a really rewarding treatment to carry out. Please take note of all of the PPE (personal protective equipment) involved, including special eyeware and ventilation.