In the first quarter of the twelfth century a German Monk, whose pen name was Theophilus, wrote a description of the techniques of making stained glass. The basic methods remain the same to this day. Glass was made by mixing sand, potash and lime and melting the mixture in a clay pot. The colour in the glass was created by adding metal oxides to the mix. Cobalt was added to create blue glass, copper for red, iron for green. Each colour had a different oxide added. This type of glass was called Pot-metal glass and it was often too dense to allow enough light through.
To overcome this problem ‘flashed’ glass was produced. This was done by taking white (transparent) molten glass on the end of a blow-pipe and dipping into the coloured glass. When the glass was blown it produced a sheet of glass that was clear with a thin layer of colour. This meant that when an abrasive wheel was used on coloured layer, the glass colour could be removed leaving the white showing from underneath - producing two colours in one sheet of glass.
Paper was very scarce and parchment was expensive so a whitened table-top would be used to draw out the full sized design. The design would be drawn out showing the position of all of the leads, this would show the shape of each piece of glass to be cut.
Each piece of glass would have the design drawn on to them, and the cut piece of glass would then be laid over the pattern so that the detail of the design could be seen through the glass. This detail would be traced, using iron oxide pigment (now know as trace); and these pieces would be fired in a small furnace to a temperature that allowed the pigment to melt and fuse with the glass, becoming part of the glass.
Sometimes several layers of pigment were used to build up different depths, for instance when there were layers of fabric or foliage to be created on one single sheet. When all the firing was completed each piece would be returned to the table ready for the glazier to complete the construction process. The glazier would use H shaped lead came in which he slotted the glass pieces. The lead provided a strong but flexible bond around the glass.
The lead (cames) were then soldered at all of the joins. Once the process was complete the panel would have oily cement rubbed into all of the joints and along the length of the lead to waterproof the panel. The panel would then be held in place by iron bars set into the masonry. From the early fourteenth century a further range of colours started to appear, due to the discovery of ‘silver stain’. This was a silver compound paint used on to the back of the glass and fired in the furnace so that a range of colours from pale lemon to a deep orange could be produce on one single sheet of glass.
Enamels in stained glass were in use by the mid sixteenth century, this brought with it a whole new pallet of many different colours also allowing artists to paint pictures in fine detail on a single sheet of glass, often set into a larger panel bonded together with H cames. These methods were very popular in the seventeenth century up until the start of the earlynineteenth century. They also saw a revival in Victorian era.In the nineteenth century, Romanticism and the gothic revival caused renewed interest in stained glass.
Important contributors at this time were:
William Morris – English (1834 – 1910).
John La Farge - American (1835 – 1910)
Louis Comfort Tiffany – American (1848 – 1910.
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