Conservation expert Val Hutchinson takes a close look at stained glass conservation problems

Stained glass windows are surprisingly robust and can survive for centuries in excellent condition. The painted surfaces providing details to the windows are, to some extent, protected by being on the inside, but damp, condensation and sometimes poor firing all contribute to paint loss.

The conservation of stained glass is a highly specialised discipline and with the best of intentions should not be undertaken by non-specialists. Even washing church windows should be undertaken by accredited stained glass conservators.

The Stained Glass Museum’s extensive collection, much of it from the 19th century, has for the last decade been under the care of Conservation Advisor Dr Sebasian Strobl, who until recently was Director of the stained glass studio at Canterbury Cathedral (1). He is now Professor of Stained Glass Conservation at the University of Applied Science at Erfurt in Germany. He generously undertook conservation projects for the Museum including ‘Bust of a King’ (c.1210), originally from Soissons Cathedral, France (Figure 1).

Healing sick glass

I recently approached the Museum to undertake an investigation and analysis of a panel from the collection. The panel (see Figure 2), from a three-light window by the Victorian firm Lavers, Barraud & Westlake (1868-1880) (2), was taken from the chapel at the Old Royal Gloucester Hospital (3) upon its demolition in 1984 and lent to the Museum.

It depicts the healing of a lame man in the New Testament accounts of St Peter & St John (Acts 3, Verse 8). One of the three panels was missing. The condition of the inside surface of the St Peter & St John panel differed from the remaining panels of the window, having paint ‘that appeared to be lifting from the surface’. The panel was removed to the conservation laboratory at the University of Lincoln for investigation and the preparation of a condition report and conservation proposal.

Visual inspection using the video microscope X25 revealed an opaque surface encrustation consisting of two layers, unevenly distributed across the panel surface and covering both painted glass and areas of glass clear of paint.

The pattern of coverage did not follow the usual pattern for deterioration of glass paint. Darker lines were clearly visible on the surface of the encrustation layer and these appeared to have been applied, possibly by brush, to accentuate the shaded areas of the painted design beneath, for example, the folds of a cloak and this was confirmed when the panel was viewed with transmitted light.

This led to a hypothesis that an opaque surface film had been applied to the panel surface and the deterioration of this film had produced the encrustation, rather than deterioration of glass or glass paint.

War-time clues

The hospital records give two interesting possibilities for the application of a surface film in the minutes of the weekly board meetings. The hospital chapel was allocated for use as an emergency ward during World War II and the internal surface of all ward windows were ‘treated with glue as an anti-shatter precaution’.

The glue was removed during 1940 as condensation caused moulds to grow. The second possibility comes from the use of blackout paint applied to all windows that could not be curtained. However, the chapel window is not specifically recorded as receiving either of these treatments. In addition, it is questionable that, in the event of one of the scenarios above, time would have been taken to apply a surface shading to accentuate the design under the coating.

After gaining permission from the owners, a sample of the surface encrustation was removed and set into resin for analysis under a high power microscope X200. This confirmed the sample as a film, possibly paint, but with no extender and not fired. Under ultraviolet light a slight efflorescence confirmed the presence of lead, which was possibly due to deterioration of the lead cames. The sample went for analysis using Scanning Electron Microscopy (SEM) and the results from this confirmed only the presence of calcium sulphate (gypsum).

While waiting for the results of SEM analysis, a series of tests were undertaken in the laboratory which gave an indication that the surface was stable. A further sample of the extremely friable encrustation was removed during a mechanical test and the sample was tested for solubility in warmed de-ionised water. The water was absorbed and the sample dispersed, but not soluble.

It is unfortunately now impossible to identify the composition of the original coating through analysis due to the cross-linking of the polymer as it has aged and formed the gypsum encrustation. As gypsum is highly hygroscopic and will attract and retain water at the surface of the glass, this may lead to an accelerated deterioration of the glass and glass paint lying under the encrustation. In view of this, it was recommended that this layer should be removed through mechanical cleaning using a soft brush and thinned out layer by layer using a scalpel while viewing under the microscope. The condition of the glass paint can then be evaluated in preparation for stabilisation of the panel.

Interestingly, the missing panel from the window has been unearthed and identified as a stained glass panel in the wall of the main corridor at the new general hospital in Gloucester. With thanks to NHS Gloucestershire.

Notes
1. Brown, Sarah and Strobl, Sebastian. ‘A Fragile Inheritance. The Care of Stained Glass and Historic Glazing. A Handbook for Custodians’ (Church House Publishing, 2002).
2. Westlake worked for Lavers & Barraud from 1858 and was made a partner in the firm in 1868, becoming the sole proprietor in 1880 (Galicki M, ‘Victorian & Edwardian Stained Glass’, 1987) 3. Gloucester Archives, Old Royal Gloucester Hospital Records, HO19. 1/25, 1911.

About the author
Val Hutchinson works as an Education Contracts Manager in the NHS.

Following completion of a Professional Diploma in Conservation Studies, Val is now working on her dissertation for the MA Conservation of Historic Objects at the University of Lincoln and has a small craft studio where she designs and produces domestic stained glass.