Renovation of unique windows at Clandon Park
Renovation has recently been completed to windows at Clandon Park near Guildford, owned by the National Trust. The windows seem to be a one-off construction of oak framing but with metal glazing bars.

The glazing bar mouldings are cast lead with an iron web inserted at the time of casting (illustrated). The glazing bars were soldered at the joints and secured to the oak frame by pouring molten lead into pre-formed slots and holes to key into the timber. Except in a few instances of later repair, there was no pin, lug or other fastening to secure the ends of the glazing bar to the frame.

The materials and construction used were unexpected as it had been assumed that the moulded glazing bars were of finely drawn wrought iron, hot coated in zinc. The structure had then been glazed with extremely thin handmade early 19th century spun glass of exceptional quality which did not exceed a 3mm thickness anywhere and in some cases was thinner. The Trust believed this form of construction was unique.

The windows may date from the early 18th century and therefore be original to the building or may have been integrated into the building around 1800. The original metal glazing bars were still in pristine condition, but some of the bottom rails in the top sashes had become bowed to an unacceptable degree such that the rails no longer met. Outside air and moisture were entering through the gap and threatening the contents of the fine interiors. Most of the top sashes were fixed and the windows may have been intended only to open in their lower part, or they may have been fastened shut as a later modification.

While 108 windows at Clandon Park could be overhauled, 13 were so fragile that padded boxes in planed softwood made to size were used to transport them to The Sash Window Workshop Ltd of Winkfield near Windsor where they could be repaired in the company's joinery shop.

Removal and repair
For the windows requiring removal for repair, temporary screens were erected on the inside; then on the outside, the centre of each window was required to be propped to support the top sash mid rail to prevent any further distortion when the window catch was released. Once the bottom sash had been removed and set aside, the parting bead was removed on one side only and a sharp blade was run around between the top sash stile and outer jamb to free the sash from the frame where they had been painted together. The sash cords were then clamped off to prevent them falling into the box frame and the ironmongery and other salvaged items labelled and set aside.

Each sash was secured with clamps before the window was totally dismantled. All the glass was labelled before removal so that it could be reused made to size were used to transport them to The Sash Window Workshop Ltd of Winkfield near Windsor where they could be repaired in the company's joinery shop.

Removal and repair
For the windows requiring removal for repair, temporary screens were erected on the inside; then on the outside, the centre of each window was required to be propped to support the top sash mid rail to prevent any further distortion when the window catch was released. Once the bottom sash had been removed and set aside, the parting bead was removed on one side only and a sharp blade was run around between the top sash stile and outer jamb to free the sash from the frame where they had been painted together. The sash cords were then clamped off to prevent them falling into the box frame and the ironmongery and other salvaged items labelled and set aside.

Each sash was secured with clamps before the window was totally dismantled. All the glass was labelled before removal so that it could be reused wherever possible. The tenon joints were then opened and the existing mid rail released. As the cut rail was prised away, the edges of the glass in the bottom row of panes was to be protected by applying strips of low tack tape. The glazing bar structure was also labelled and removed from the frame into which it had been soldered with lead. The excess lead in the glazing bar rebates was then drilled out to enable later refixing. The deformed rails were then removed and replaced using best seasoned English oak heartwood ton match the original profile section, depth, breadth, joint configuration and straightened length..

Re-assembly
The glazing bar framework was offered up to the sash boxes and the position and depth of the rebates required in the new mid rail was marked. The rebates were then formed and two 1/4 inch holes drilled in them. to take the molten lead. The glazing bar framework was then refitted by pouring molten lead into the rebates then leaving the lead to cool. If existing glass would correctly fit, it was reused. Where this was not possible, new hand made cylinder blown glass was used. The sashes were left laid flat for two weeks to allow the putties to harden sufficiently for reinstallation.

The works formed part of a grantaided English Heritage project which also included re-roofing and the replacement of defective stonework on this Grade I house. The Trust had acquired the grand Palladian Clandon Park in 1956. The house, particularly well known for its magnificent Marble Hall, had been designed by the Venetian architect Giacomo Leoni around 1730 for the Onslow family, three of whose members served as Speakers of the House of Commons. In the 1920s it was owned for a time by the connoisseur Mrs David Gubbay before passing to the National Trust.