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Very little has changed since Medeaval times and we use essentially the same techniques.

In the first quarter of the twelfth century, a German monk, who adopted the pen name Theophilus, wrote a description of the techniques of making stained glass. The basic methods have hardly changed. Glass was made by melting sand, potash and lime together in clay pots. lt was coloured by the addition of metallic oxides - copper for red, iron for green, cobalt for blue and so on. This is called pot-metal glass. Pot-metal glass, especially red glass, was often too dark to transmit much light. To overcome this, 'flashed' glass was made by dipping a lump of white glass (transparent) on the blowpipe into a pot of red glass and then blowing, This provided sheets of glass with a thin surface layer of colour. Later, parts of this layer could be removed by grinding with an abrasive wheel; this produced two colours, red and white, on the same piece of glass.

Because paper was scarce and parchment very expensive, the full scale outline of the design for a stained glass window was drawn out on a whitened table top. The designer would indicate the principal outlines of his drawing, the shape and colour of the individual pieces of glass to be used, and the position of the lead strips (calmes) that would eventually hold all the pieces of glass together. The panes of coloured glass were cut to shape with a 'grozing iron' and laid on top of the drawing.

Through the glass, details of the drawing - faces, hands, drapery etc. - could be seen and these details were traced with an iron oxide pigment on the surface of the glass. After painting, the pieces were fired in a small furnace for sufficient time to fuse the paint to the surface of the glass thus becoming part of the glass, and then relaid on the table and assembled by the glazier, using strips of lead H-shaped in section, which allowed the glass to be slotted into the grooves on each side. The lead provided a strong but flexible bond.

The intersections of all the lead strips were then soldered, and an oily cement was rubbed into all the joints in order to make them watertight. The panels were then held in place in the window openings by a grid of iron bars set into the masonry. From the early fourteenth century a further range of colours varying from a pale lemon to a deep orange could be achieved on one piece of glass through the discovery of 'silver stain', a silver compound painted on the back of the glass and then fired in a kiln. By the mid sixteenth century many different coloured enamels were being used. As a result, windows began to be painted like easel pictures on clear glass of regular rectangular shape, with lead calmes no longer an integral part of the design. These methods prevailed from the seventeenth to early nineteenth centuries. However, the earlier techniques were revived in Victorian times.

These days very window starts as a full-size cartoon drawn in the studio on tracing paper. The coloured glass is then selected from a sample range of over 1500 types of glass to conform with the designer's conception and the position and purpose of the window. The glass is cut to size with a glass cutter. Awkward curves can be nipped ('grozed') with a pair of grozing pliers.

The design is applied as a black or brown paint which is a mixture of metal oxides, powdered glass and gum. The artist mixes it with water on a thick glass tile. Solid lines are painted thickly, carefully tracing the design from the cartoon. Thinner washes are left to dry and then dusted with a badgerhair brush to give fine shading effects. Finished pieces are then stored in glass racks to await firing in the kiln. The painted glass is laid on a heat resistant material and fired at a temperature which fuses the paint to the glass. If silver stains are required these are applied to the back of the glass and fired at a lower temperature.

With the recent deveopment of large electric kilns it is now possible to make pieces of painted and enamelled glass 2 meters by 1 meter which can then be toughened to conform to safety regulations. You can see examples of this on the website.