The worst cases of decaying frames can be replaced with exact replicas, with or without double glazing. One typical customer, whose windows let in draughts but refused to open, paid pounds 1,600 to have five 125-year-old sashes sympathetically restored. “It’s still a cheap way to add value to a period house,” Giles says.Meanwhile, replacement-window companies (who charge about pounds 600 to double glaze a sash) continue to offer persuasive arguments. Plastic frames, they say, never need painting; and double glazing prevents heat loss. The whole ensemble was an efficient system of joints, pegs, cords, pulleys, counter-balancing weights, shutters and brass catches. The timber was deal or Scots pine, cut from mature trees, highly resistant to rot and far superior to anything available now.

And what is left of hand-made glass is a finite resource – a few modern craftsmen are making reamed and seeded glass, but you can’t reproduce age.Giles’s company, the quirkily named Sashy and Sashy (“if you use the word windows in a trade name everyone assumes you are selling double glazing”), contributed to the English Heritage video Framing Opinions, by demonstrating the conservation-friendly art of taking rattles and draughts out of time- worn windows. But according to a window conservation expert, Giles Hamilton, the same could be said of any example of period glazing.”A window is like a piece of furniture,” he says. “And if you were to commission a cabinet-maker to reproduce a Georgian or Victorian sash window, you would have to ask for a piece of furniture that could be left out of doors in all weathers and temperatures and survive anything up to 200 years of neglect.”He points out that making a sash window in, say 1850, involved around 10 different trades. The conversion of her dining-room window, however, cost a relatively modest pounds 350.In cities such as Glasgow, which saw their major expansion in the late Victorian era, coloured panels are a common feature of Victorian sash windows, and because of their outstanding pictorial qualities, they are readily perceived as works of art. The green panels, meanwhile, have been incorporated into an interior door. Further examples of stained-glass artistry line the upper sashes of one of the bedroom windows, but Doreen is waiting for “a lottery-win situation” before tackling restoration.

Now she has a beautiful pictorial window and a view of the garden. “Some people love the way coloured glass images animate an interior,” says Sally Rush, a glass historian “But modernists hate it. Others associate it with a rather vulgar period of design, and there’s a common myth that all stained glass looks churchy and casts a dim, religious light.”To Doreen Logan, an art teacher, it’s no myth. When she bought her Edwardian house in Glasgow 11 years ago, she removed some of the stained glass lights from a sash window in her dining room, precisely because the design – a delicate Art Nouveau tree of life – darkened the interior. “It was absolutely horrible to have so little light and no view in such a big room,” she says.She came to a reasonable compromise by removing two sections of plain, green pebbled glass from her six-panelled sash window and replacing them with clear “restor-ation” glass. “I can’t believe that anyone would ever dream of removing or destroying such a beautiful thing.”But this is one period feature where personal taste plays a major part in its survival.

Broken pieces of the jigsaw were either replaced with new or reclaimed glass or carefully bonded together The whole process cost the Skinners around pounds 1,000 They think that it’s money well spent “It’s a work of art,” Eileen says. Some go for the historically correct, others prefer modern abstract designs and geometric shapes.” Common commissions include coloured panels for front doors, room dividers, conservatories and bathroom windows.In the case of the Skinners’ Leda and the Swan, the original glass mosaic was carefully taken apart and reset in a new lead framework. For the client, Caroline Swash says, commissioning glass artworks for the home is an opportunity to add a contemporary dimension to a period property. “It’s important is to take the rhythm of the architecture into account, but otherwise the choice of design is a matter of personal taste. The range of coloured and tinted glasses now available is also unprecedented, though most of the material comes from France, Germany and Poland.

The only 19th-century factory in Britain, still producing hand-blown, pot-coloured glass is Hartley Wood in Sunderland, a firm founded in 1892 and now run as a co-operative.One of the myths about stained glass conservation, Susan says, is that old glass cannot be matched with a modern equivalent of the same colour. It is true, however, that the glass is expensive and the restoration work is very laborious. People are put off by costs, but the Stained Glass Partnership has, none the less, seen a recent increase in domestic restoration commissions. The only damage that cannot be remedied is caused by cleaning glass with abrasive chemicals (which scratches surface designs) but even a missing window or door panel can be remade.To most glass artists, restoration is bread-and-butter work; the meaty jobs are in originating new designs.