Metal conservation, cellulose nitrate and the Oddy Test
Resource type
Book chapter
Creator (person)
Eggert, Gerhard
Bette, Sebastian
Ziegler, Julia
Korenberg, Capucine
Kuiter, Rebekka
Stelzner, Jà¶rg
Date published
2019
Abstract
Conservation materials such as coatings, adhesives and consolidants are often applied to museum objects and, as such, are present in stores or display cases. It is necessary to check they do not emit volatiles that are harmful to object materials and one way this can be done is with the Oddy test – a material screening carried out at an elevated temperature. Cellulose nitrate (CN) is routinely used by conservators as an adhesive and a lacquer for silver objects. A commercial ready-to-use variant of dissolved CN – HMG – was Oddy tested by the State Academy of Art and Design Stuttgart (ABK) (where it failed) and the British Museum (BM) (where it passed), the only difference being that at the ABK the sample had been left to dry for two months, while at the BM only three days of drying were allowed, as per the standard BM protocol. When the HMG samples were dried for two months they consistently failed the Oddy test at both institutions. Traces of solvent left in the resin might act as a stabiliser (radical scavenger) hindering CN decay. Further Oddy tests on Paraloid B-72 showed that, when dissolved in ethyl acetate and cured, traces of solvent in the resin corroded the lead coupons. This demonstrates that resins must be fully cured before their volatile emissions are assessed and it is necessary to re-consider the drying of solvent-based products in the BM standard Oddy test protocol. In the Oddy test for CN, silver cyanide nitrate was detected on the silver coupons. Even tests at room temperature showed cyanide compounds formed on silver when exposed to HMG. CN products could pose a risk to museum artefacts and conservators should carefully consider their use and select alternative tested products as much as possible.
Book title
METAL 2019 - Proceedings of the Interim Meeting of the ICOM-CC Metals Working Group
Editor
Joseph, Edith
Brambilla, Laura
Chemello, Claudia
Pagination
125-131