Stained glass making began life as a Christian art form a very long time ago. The instructions that the monk Theophilus wrote in 1100 AD have changed little over the previous 900 years. Most of the glass in St Clement owes its origin to the Gothic Revival that swept Britain in the nineteenth century, and although the history of the windows is interesting, the purpose of this guide is more “to illumine men’s minds so they may travel through it to an apprehension of God’s light”, as one medieval French abbot put it.