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How stained glass was originally produced

The process of stained glass has been around for hundreds of years, but how was it originally made?

Making the ’Cartoon’

The first stage of any glass production would begin with an artist, where they would create the initial sketch of the finished stained glass product. This could be built up of a number of colours, shapes, designs and more and this process of drawing the design was producing ‘cartoons’. Any shapes, colours or signifying marks were indicated onto the initial design.

Cutting the glass

Different colours of glass can be chosen for all parts of the design, and when this is confirmed the outline of each glass piece is painted with white lime wash. These glass pieces are cut into rough outlines of their final shape by the use of a dividing iron. This causes the glass to break away, leaving the original design.

The pieces of glass are further reduced to the optimal size from the use of a grozing iron. This is an iron bar that is used to chip away at the edges of the glass.

Painting the design

After the glass pieces of the structure were both cut and shaped into their desired size, they were often painted with a pigment made from the mixture of ground copper and iron oxide, along with powdered glass.

A number of elements could be added to then help apply this pigment to the glass: the most common choices were wine, vinegar and even urine! Once this had been painted, the glass pieces would be entered into a wood-fire, which is called a kiln.

Glass painters would use a special kind of paint, which would be made from glass particles that are suspended in a liquid binder.

Using lead
The pieces of glass were then held together from the use of a narrow strip of lead, forming a panel. Lead was used mostly down to its flexibility, providing a large amount of adaptability that was often required to fit the various shapes of glass into their position.

Introducing glazing
After all the individual glass pieces are painted and fired, they’re all placed into set positions onto the original cartoon sketch. This allows the glass pieces to all fit together, forming a panel. In the Middle Ages, the use of a hammer and knife were used to put these together.

Cementing it in place

After the glazing process, the panel would be cemented into place in order to help with securing the glass within the lead, waterproofing the window. A liquid cement is then applied using a brush, covered by a layer of chalk or sawdust. This helps to absorb any excess liquid.

Finally, the panel would be scrubbed down with a dry brush.

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