Catherine Coueignoux presented an exciting treatment of the Augustus Rex (c.1750) writing cabinet in the collection of the Victoria & Albert Museum (W.63-1977 http://collections.vam.ac.uk/item/O74665/writing-cabinet-kimmel-michael/# )
The elaborate ormolu mounts had been previously re-gilded. Before treatment were coated with a thick layer of dirt and dust over a shoe polish-like wax treatment, which was possibly added to dull the appearance of the bright new gilding. All other metal components were corroded, and the wood and marquetry had all been stripped and refinished. Curators wished the treatment to result in a bright, nearly-new appearance as it may have looked when newly restored (the previous refinishing and regilding probably occurred while owned by the Rothschild family).
Spotty corrosion on metal components that could not be removed was treated locally where possible. EDTA gel and BCA gels were tested but unsatisfactory- cleaning not enough, or too well. Coueignoux was able to use rottenstone to spot clean dark areas, leaving a layer of light corrosion sympathetic to surrounding areas. In some places, the corrosion spots were left untreated.
The removable ormolu mounts were cleaned using dry ice pellets, a new method for the lab. Their system uses a block of CO2 dry ice which is shaved into pellets and sprayed onto the surface of the object using an air compressor with a custom nozzle. The CO2 pellets expand on contact, providing a gentle mechanical cleaning. By moving quickly along the surface, they were able to avoid excessive cooling that would result in condensation. Acetone and a hairdryer were on hand to remove any condensation that did form. Other labs using CO2 cleaning include the Getty and the Smithsonian.
In the case of the ormolu mounts, CO2 cleaning was fast, safe and effective and removing the unwanted wax and dirt- 150 mounts were cleaned in only seven hours! Obviously this method is not appropriate for many objects and materials, but may be a convenient choice for more conservators in the future.