Surface Tension

All liquids have surface tension – the attraction between molecules that, on the surface of a liquid, causes the liquid to behave as if it had a thin skin.  Surface tension, for example, is why water drops on a slick surface will “bead” up.

Surface Tension

Surface tension strength is different for different liquids.  Mercury, for example, has very strong surface tension.  Acetone, in contrast, is very weak. The strength of the surface tension of glass at 1500° F is somewhere between the two.  The strength of the surface tension determines the natural height of the liquid when allowed to spread.

Surface Tension = Different Liquid Heights

For glass at 1500° F, that height is about ¼ inch (6 mm) – which is the same height as two standard layers of glass.  Understanding how this impacts the results when fusing is one of the most important lessons a fused glass artists can learn:

  • If your project has less glass than in two complete layers (for example, a single layer with only a few design elements), the edges of the base glass will begin to pull up as the glass tries to achieve the ¼ inch thickness.
  • If your project has close to two complete layers (for example a single layer of  glass with a complete second layer of design elements), the glass will flatten when fully fused – but will maintain its overall shape.
  • If you have more than two layers of glass, the glass will spread when fully fused (unless you contain it with dams)

Here’s a simple illustration showing the above three examples:

Glass Heat and Volume

But what if you want a fully fused design – but you want it to be a single layer thick?

One solution is to fuse the thick project and then grind it down with coldworking equipment, such as a reciprocating lapidary grinder like this one:

Reciprocating Lapidary Grinder (reciprolap)

That approach requires expensive equipment, a lot of time, and you end up wasting a lot of material by grinding it away.

With kiln-pressed glass, you probably already have everything you need, the work is all done in the kiln, and there is no wasted glass.

Curious how it works?  Just click the “Overcoming Surface Tension” link below and we’ll get started!

Back to Kiln-Pressed Glass Start

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