Stained Glass - Art at the Glass Surface
Cambridge - Monday 4th and
Tuesday 5th September 2017

Claire Boselie

article posted 17 May 2017

Claire Boselie holds an MA in Conservation Studies with a speciality in Glass Art from the University of Antwerp. During and after her academic studies, she has worked for and interned at various national and international institutes, including the Nationaal Glasmuseum in Leerdam, the Netherlands, the University of Antwerp, Belgium, Clerkin Higgins Stained Glass Inc. and The Metropolitan Museum of Art, currently known as ‘The Met’ in New York City, U.S.A.

Commercial transparent cold paints used for inpainting on glass: a research into degradation parameters
Claire Boselie*1, Dr. Olivier Schalm2 and Prof. Dr. Joost Caen3

1,2,3 University of Antwerp, Faculty of Design Sciences, Department of Conservation Studies, Blindestraat 9-13, 2000 Antwerp, Belgium.

Glass can be decorated with a diverse range of materials in which glass paints and stains are the most commonly used and contain their own unique set of properties. For instance, the grisaille paints, which are generally based on a ground, lead-rich silicate, mixed with metal oxides, provide an opaque coloured layer on top of the glass substrate. Enamels, consisting of a ground, batch-coloured glass, result in a more translucent decoration after firing. Moreover, stains, which consist of metal compounds (generally silver or copper) that are dispersed as a powder in a clay based medium, will in turn produce a transparent wash of colour inside the glass substrate that is made possible through ion exchange.

Transparency is a quality that is inherent to glass itself, and as a result, the glass conservator naturally faces this prevalent obstacle more so than other conservators. For damaged glass substrates, enamel paint, or stains, glass conservators tend to reach for commercial transparent cold paints to in paint losses. These transparent cold paints, however, are arts and craft materials and are not designed for conservation purposes. Because of this, little is known about the exact composition of these paints, their longevity, and colourfastness, which may hold consequences for the usage in conservation treatments in terms of durability and reversibility. Therefore, not only should the stability of the different brands of cold paints be researched, but also the differences between the various colours within those brands.

The preliminary research, made by former colleagues V. De Crom and J. Claessens in 2005-2006, that this paper’s research expands on, involved a series of colourfastness tests of three brands of commercial transparent cold paint—‘Lefranc&Bourgeois’, ‘Talens’ and ‘Marabu’— (they made the research, I hope I fixed the problem). During this research, mock-ups were made to measure before and after exposures with photo spectroscopy to identify potential loss in colour. The original mock-ups were then rehung (rehung is sort of a slang term. Can you use another word?), but never re-evaluated until this research in 2013-2014. In addition to the re-evaluation of the original mock-ups with UV-VIS spectroscopy, two in-situ case studies were examined;a new test case was set up in a climate chamber, and climate research was executed with various types of data logging equipment at the different test case locations to provide insight on the stability and colourfastness of four brands of commercial transparent cold paints —‘Lefranc&Bourgeois’, ‘Talens’, ‘Marabu’ and ‘Pebeo’—.