What makes glass “spread” ?

[EclecticTreasures]

I have just full-fused a kiln load of “blanks” that I will use as the base for some pendant designs. They were all two layers of glass: some 1 inch square, others 1 1/2 inches square, others 1/2 inches by 2 inches. Some of them maintained their original cut size – while others “spread” and ended up measuring larger than their original size – although they “spread” evenly. For example, one of my 1 inch squares ended up being almost 1 1/8 inches square.

What makes some pieces get larger while other remain true to the original measurements? How can I keep the spreading in check?

Thanks,
Barb

[Anonymous]

At fusing temperatures, the glass will naturally flow until it is about 1/4″ (6 mm) thick. That’s two layers of typical glass.  If you stack three layers, it will flow. If you put in one lone layer, it will draw up.

This is caused by surface tension in the molten glass.  It is the same force that causes water to bead up on your kitchen counter.  When you put more water on the counter the drops don’t get taller – just wider.

---

Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com

 

[Juno123]

Bullseye Technote #5 helped me with this (Volume & Bubble Control).  It has good diagrams and explains the process well.  You could try to look it up on the internet; I got a technical Bullseye Book at my local glass company.  You could dam the peices to keep them from spreading.  Hope this helps.

[EclecticTreasures]

Ahh- that makes sense as to why some of my pieces get larger than others – glass thickness or number of layers.

This is such a great forum – ask a question – get an answer!!!

Thanks, Paul!

Barb

[EclecticTreasures]

Great resource! Thanks for pointing me in the right direction. I have looked at the Bullseye Education site before, but had forgotten about it. It’s in my bookmarks now!

Thanks again,
Barb

[steve worcester]

Understand that it only is relevant to undamned pieces. If you shore up the sides (technically) it will maintain that approximate height (thickness)

Steve Worcester

http://WWW.TURNINGWOOD.COM

[Author]

Posts