To create nIII’s inscriptions, medieval glaziers cut out strips of white or yellow glass, coated it with black paint and then picked out the shape of each letter. This allowed light to shine through the glass and for viewers to see the letters as white or yellow shining out against a black background. Inscriptions the length of those found in nIII required at least four separate pieces of painted glass.
As glass slowly corrodes over the centuries, paint on the surface can be lost. In the case of extreme paint lost, inscriptions are left looking like strips of glass with no letters on them at all. However, it is often possible to recover the lost lettering by directing raking light at the glass, which allows subtle differences between surfaces to become visible.
To make lettering visible again to viewers, today’s conservators do not paint on the original glass. Instead, they paint on very thin strips of glass that will be attached behind the originals. Once these “backplates” or “plates,” as they are called, are in place, the lettering will be visible when the light shines through the glass.
In 1989, Canterbury’s conservators installed backplating behind many of nIII’s inscriptions. Unfortunately, they did not have a medieval Latinist working with them, and much of the backplating they installed was mistaken.
In 2022-23, the stained glass studio was given permission to correct three of nIII’s inscriptions. To begin, the exterior face of lead is cut away to allow access to the inscriptions whilst leaving the rest of the panel intact. The 1989 plates are separated from the historic glass and archived.
New backplates are created using the information gathered from the raking light investigations. The new paint on the plate is fired to high temperatures in order to fuse the paint onto the surface (medieval glaziers, too, fired their glass in a kiln to fuse black paint to glass).
As the original glass is not always flat, plaster casts are taken from the original glass. The plates are then kiln-moulded to perfectly fit the medieval contours. The plate and the original glass are next sealed with silicone at the edges to create a small unit. These units are reinserted into the panels. When done carefully, backplating can make very dramatic differences in legibility.
Because the inscriptions are painted on more than one piece of glass, they were sometimes mixed up in the course of restoration. This happened with the inscription found on the second Hugh of Jervaulx panel. Some of the strips of glass making up the inscription in the top line had broken. The pieces were re-assembled incorrectly, probably as far back as 1857. The 1989 backplating also had inaccurate readings and was poorly painted.
Examination of the original glass under raking light, along with consideration of the metre and rhyme required by the verse form utilized in these inscriptions, made it clear that the inscription should read SPES DESPERANTI SVPEREST IN SANGVINE SANCTI, or “Hope remains for the hopeless in the blood of the saint.” The broken pieces of glass reading SPES DE and SPERANTI were carefully glued together (using silicon) and put in their correct positions. New backplating was then painted and installed. It is especially satisfying to be able to correct this inscription as it is in the bottom circle of the window and quite close to viewers.