Tuesday, 15 November 2011

Designing for Strength

Principles of Design Practice for Stained Glass, 1

There comes a stage when each of us moves from using patterns developed by others to trying to realise our own vision. This is the time where in attempting to reproduce an image from our mind or from natural and man-made forms that we begin to encounter difficulties with the medium of glass and lead or copper foil.

There are a number of principles that should be kept in mind while designing, or at least referred to when the design is reaching its final stages. This series of notes is an attempt to outline a number of the most important points in designing glass panels, especially larger ones.
Structural strength
The panel needs to be strong to last for a long time. Glass is a very resilient material; so is lead and solder. It would be a shame to design a panel in long-lasting materials that will not last because of the design and construction. There are some things to remember about creating a strong panel.

The strength of a panel is in its glass.

Glass in compression is stronger than steel. It is only when it is in tension that its weakness - or fragility – becomes apparent. So the structural arrangement of the glass needs to be such that each piece of glass supports its neighbours. It also needs to use shapes that are strong.

Avoid the following shapes:
  • Hour glass shapes – those where the ends are wider/larger than the middle - will crack at the narrowest part. If the shape – usually a negative or background one – is necessary, break it up into smaller pieces that make sense in the whole design. It is also possible to add details that will break up these shapes, but be careful that the details do not detract from the whole.
  • Exaggerated, deep inner curves will crack at apex of curve. If unavoidable, you should consider adding design lines where the glass would break anyway, or moving elements closer together so they almost touch to avoid the single deep inner curve.
  • Thin long and tapering glass pieces will crack at the point or be covered by the lead or copper foil. Where you need to have such shapes, try drawing the lead or copper foil lines on the design. You can do this on a piece of tracing paper to avoid messing up your original design. This will show you how the finished panel may look. Alternatively, you can divide the long tapering piece of glass into several pieces so that any flexibility of the whole panel does not break the long thin piece. Short thin pieces are not so likely to be broken by any movement of the panel.

Lines radiating from a single point provide weak areas. This is due to long thin pieces of glass being liable to breakage. Break up long thin pieces of glass with lines. This ensures that the length of the glass is in a strong relationship with its narrowness.

Avoid “hinges” - lines that run from edge to edge – as that provides an area where the panel can bend. This is why windows made up of rectangular quarries need so much support and even then over time begin to concertina.

Don’t over complicate the cut lines. This makes for difficulty in cutting the pieces. Also the more difficult it is to cut the pieces of glass, the more likely it is to fail by breaking after being installed.

Elements of Design: