Early in 2020 the Cathedral’s Conservator was tasked with lifting the carpeting in the Baptistry and giving a condition report on the mosaic underneath. What follows is an account of her experiences to-date, following that report:
There were a few issues that immediately stood out when the carpet was removed. An initial glance over the surface of the mosaic identified large areas of salt efflorescence, the majority of which were located on the western side of the mosaic, behind the font and stone pedestal. There are also a total of four areas of loss, where tesserae (mosaic tiles) have come loose and a fill material has been put in for stabilisation purposes. The majority of the fills are lime based and allow for better breathability, however, there is cement fill that is significantly older than the others. This fill also goes underneath the surrounding mosaic tiles, causing undulating waves. Areas to the south and north east of the font are hollow, where the tesserae have become detached from the backing mortar due to the salt efflorescence.
Closer inspection revealed the presence of an acrylic based varnish that had been applied over the entire surface of the mosaic and stone steps that lead to it, as well as on some, but not all, surfaces of the font itself. Enquiring with long standing members of staff as to how long the varnish has been on the mosaic for, it was found to have been applied initially some 35 years previously by an ill-informed but well-intentioned member of staff. The product was mopped onto a large proportion of the stone floors in the Cathedral, as a way of offering protection and additional protection. The majority of the varnish within the Cathedral had been removed by the cleaners in previous years using Nitromors, but due to the carpet, it was not known that the varnish was also covering the Baptistry mosaic.
Consolidated dirt trapped between continually applied layers of discoloured varnish left an overall murky brown appearance to the mosaic, in some parts obscuring the design and colour of the original tiles completely.
A project was started in November 2020, on the Baptistry mosaic, to remove the varnish to allow better surface breathability for the tesserae, and to stabilise any inappropriate fills that may be causing problems to the surrounding mosaic. A core sample has been taken to identify what the mosaic could be laid on, as there is speculation that the mosaic was laid on a concrete screed in order to level the floor off and provide additional strength.
Cleaning tests revealed that poulticing with acetone saturated cotton wool, followed by light mechanical cleaning with a toothpick or spatula was the most appropriate and least damaging method of removing the varnish. Areas where the varnish was thicker had to be left soaking for longer to adequately soften the top layers of varnish, before they could be removed using a no. 9 scalpel blade or spatula.
The current phase of the project is still ongoing, but will be finished by March 2021. Funding for this phase has been graciously provided by Historic England and The Department for Digital, Culture, Media and Sport (DCMS). If you’d like to keep up to date with this project, you can follow us on Instagram at ‘the_works_department.’
Naomi’s work to date has slowed the rate of decay in this wonderful mosaic, uniquely designed by Chester’s Dean Howson. However, this is only an initial phase of a bigger project. To truly save this mosaic from eventual destruction many more years of work and investment will be needed. The Cathedral is fortunate to employ highly skilled conservation practitioners who we are incredibly proud of and whose work will help to preserve our fine Cathedral for future generations. Your support is always needed and greatly appreciated to help ensure these skills are kept alive and the Cathedral fabric protected.
Clerk of Works