Conservation of niello

Marie-Odile Robbins <westdean [at] pavilion__co__uk> writes

>  ... I would like to
>  enquire on the approaches and treatments professionals have
>  taken to preserve and/or restore niello.

Because of the unstable chemical nature of most recipes generally
containing frozen molten sulfur and lead, the restoration should
absolutely avoid any thought of heat treatment.

The main condition to obtaining a good surface finish is to polish
the top layer after melting the mixture only once, so by remelting
you are very likely to release internal tension resulting from
cooling the first time and polishing, provoking evolution of sulfur
gases and obtaining the opposite to the wanted result. Furthermore
the melting will cancel all possible future study of historical
composition's research.

Certainly degreasing and acrylic protection or even local
restoration is most likely to match the aesthetical and ethical
aspect of those unstable materials.

D. Cottier-Angeli   Geneva
Jeweller and Metals Conservator
Coordinator of the Metal Conservation Laboratory of the Fine Art
Museum in Budapest

                                  ***
                  Conservation DistList Instance 11:94
                   Distributed: Tuesday, May 19, 1998
                       Message Id: cdl-11-94-011
                                  ***