After securing the contract, a schedule of work is agreed with the client.
The scaffold is checked to ensure the utmost site safety, and a risk assessment completed.
Detailed assessments are made of the condition of the stonework as well as the stained glass itself. Any issues raised are reported to the architect.
All panels are labelled using the CVMA numbering system.
Internal and external photographs are taken
and details of poorly fitting panels noted.
Excess mortar must be removed in order to take detailed sizes
Accurate templates are taken of the intricate profile of the stonework.
The Removal Process
Mortar is removed from the glazing groove using hand tools, and the panels released from their support bars
by cutting free the copper tie bands.
The support bars are removed and set aside
and all exposed openings securely boarded.
Back at the Workshop
Panels are safely stored on 'A' frames separated by foam sheets.
Pre-restoration photographs are taken on a vertical light box
and meticulous rubbings made of each panel.
Detailed cut lines are produced
which are used for the manufacture of the protective glazing.
Conservation of Stained Glass
Fractured pieces are bonded where possible
but where necessary severely damaged pieces are replaced.
The damaged piece is cut along a garment fold so that a newly inserted lead will be unnoticeable, and the broken pieces removed.
Relacement glass is found to match the original in colour, tint and texture. A pencil sketch of the new piece is made
and pigment applied to the new piece using an appropriate style and technique.
We apply a trace line first, then add washes of appropriate depth and intensity
The new piece is signed and dated discretely on the reverse
before being inserted into the lead cames and sealed with black putty
Internally Ventilated Protective Glazing
Isothermal glazing is used when the stained glass panels require removal for external environmental reasons
Framing the Stained Glass
We shape and fit manganese bronze channel around the border lead cames of each panel.
The bronze channel is soldered together with corner backing plates on each angle.
Discrete fixing brackets are riveted to the frames
Lead tape is attached to the reverse side of the frames to prevent light from showing around the perimeters.
Each panel is then photographed again on the light box
and all interventions recorded on the rubbings using CVMA-recommended annotations.
External protective glazing is created taking the main design lines from the stained glass lead matrix
in order to emulate a stained glass window from the exterior. It is modified to allow for parallax.
Each cut piece of sheet glass is kiln fired to distort the surface
and to break up the smooth reflection from the outside.
These pieces are then leaded together using cames of appropriate weight, size and profile, and then 'cemented' on both sides
- a process which requires a linseed oil based compound to be brushed under the lead cames rendering the panels solid and waterproof.
Panels are left to dry, then cleaned and polished.
Copper fixing ties are soldered to the panels at appropriate points.
New lead cills are made in the workshop using lead sheet
which is shaped and dressed to fit the stonework.
New window guards are manufactured using grade 304 stainless steel welded wire mesh
with aperture spacing of 75mm x 12mm x 12swg running vertically, and bordered with grade 304 6mm stainless steel round bar.
All window guards are TIG welded and finished in polyester black powder coating. They are wrapped in protective plastic for transportation.
Fitting the Window back into Position
The protective glazing, window guards and framed panels are transported to site.
New non-ferrous support bars are placed in a similar position to the original tie bars. The protective glazing panels are mortar pointed into the glazing groove and attached to the bars with their tie bands.
The window guards are fixed in position to the exterior of the protective glazing using black powder coated stainless steel clips and blackened stainless steel screws.
The lead cills have been placed in position prior to fitting the protective glazing, they are now adjusted and shaped to fit snugly round the mullions.
From the exterior, the guards fit neatly into the stonework and the protective glazing resembles the original stained glass
The frames enclosing the stained glass are fixed to the internal stonework with care,
using brass screws into plastic plugs,
ensuring that a gap exists both at the top and base of each light to allow constant airflow around the panels.
The lead flanges are flattened back to the stonework.
A photo taken with flash, to highlight the outline of the frames
and to illuminate the lead flashing
which, without a flash, hides all light surrounding the tracery panels.
Finally the window is brushed down and cleaned, all debris cleared away from the site,
and the completed window photographed in-situ.
Beverley Minster Window n23 – Project Overview
Conservation and Isothermal Protection of this high quality stained glass window.
After success in the initial tender process, the starting point for this project was to take the original condition report and architect’s specification and use these to compile a scope of works that reflected the true extent of the job.
As the panels were distorted, it had initially been thought that the window would require extensive re-leading. After closer inspection however, it was judged that incorporating the panels into a protective glazing system would remove the necessity of widespread re-glazing, resulting in a less intrusive conservation scheme and ultimately reducing the original contract sum for the client.
The scope of works would include removing all the main light panels and tracery lights for specialist conservation cleaning, minor restoration and limited re-leading. The panels were then incorporated into manganese bronze frames as part of an internally ventilated protective glazing system. New plain glazed panels following the main design lines of the stained glass were manufactured and fitted within the existing glazing groove previously occupied by the stained glass, which was then mounted – within its bronze frames – internally, allowing a constant airflow around the panels. Black powder coated stainless steel window guards were fabricated to fit within the intricate profile of the stonework.
Once all the work was completed to schedule, a detailed post-conservation report was provided to the client.