The story of why medieval stained glass survives in some places and not in others is an intriguing one and not always well understood. This is something that I have recently written about in an article for Historic Churches, to be published in June.
The Reformation of the mid-sixteenth century turned the tide on the use of imagery in the church and it is often thought that windows were smashed when the altars were stripped and statues of saints removed and destroyed. It is not clear how much this was actually the case, and, as Richard Marks points out in his Stained Glass in England during the Middle Ages (1993), attacks on stained glass ‘should not be overestimated’ and stained glass windows ‘were permitted to remain intact because of the expense of replacement’ (pp. 231–2).
We do know that pictorial medieval stained glass was destroyed in Wales during the 1640s, but a great deal was probably thrown away because of its gradual decay and neglect, even as late as the mid-nineteenth century. My article then gives examples of the ways in which medieval stained glass was retained and restored in medieval churches during the nineteenth century. Sometimes fragments of medieval glass were incorporated into new compositions, and often fragments were simply leaded together as a jigsaw without any pictorial meaning. In fact, these panels strike me as essentially abstract works, made in a period before abstraction was taken up seriously in visual art.
Historic Churches is an annual magazine and has published a number of useful articles on stained glass in recent years, particularly in relation to conservation. Many of these articles are available online, including a useful article by Sarah Brown that provides useful context on the iconoclasm of the Reformation and the Civil War in England. Perusing these articles I came across an article on the nineteenth-century Welsh pioneer David Evans, something that I am sorry to have missed a coupe of years ago, as it would have deserved a reference in Stained Glass from Welsh Churches.