Fish- scale glazing looks complicated to do and is. It was adopted for three reasons. First if you have to glaze a curve, it is cheaper than using curved glass. Secondly, it allows for some ventilation around the curve. (Loudon and fellow designers were very exercised by the question of ventilation.) Thirdly the curve of the glass means that rainwater runs away from the glazing bar, rather than onto it, thus protecting the metal.
The “scales” sit on a flange in the wrought iron glazing bar held by putty and more putty is applied on to top to hold the glass fast. The puttying everywhere is in very poor condition.
About 20% of the panes are missing. The glaziers will have to remove all other panes which are loose or which the metal workers feel they have to get beneath to clean.
Historic England has analysed the glass in detail. There are all types of glass from all periods in the last 200 years. The bulk of replacement glass will be narrow reeded. This is no longer manufactured but there is some supply taken from a Pinery at Felton Park demolished in the 1950s, and from reusing glass removed from the casements which will be clear glazed. If this runs out, we shall use clear horticultural glass. After restoration, the greenhouse will still have a motley and mottled collection of glass types, reflecting its history.
Cheshire Stained Glass will undertake the glazing work.