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Polarisation question
Posted: Fri May 09, 2003 3:28 am
by Lauri Levanto
I have tested flat pieces with polarized glasses.
Most of my work is 3D, however, and the
thickness variation seems to affect polarisation.
(Or have I annealed all my reliefs wrong?)
-lauri
Re: Polarisation question
Posted: Fri May 09, 2003 9:27 am
by charlie holden
lauri wrote:I have tested flat pieces with polarized glasses.
Most of my work is 3D, however, and the
thickness variation seems to affect polarisation.
(Or have I annealed all my reliefs wrong?)
-lauri
Complicated changes in depth, especially if there are sharp corners -- like square voids or holes that pass all the way through the piece -- make annealing much more critical. If I'm annealing a piece that has a negative relief design I double my annealing schedule. If the negative relief is blocky or square I slow it down even more.
The stress tends to concentrate around the negative space. Think of the ways a solid glass block is pushed and pulled as it tries to contract in volume as it cools down. It is trying to contract across its entire width, bredth and depth -- in other words it's trying to shrink in towards its center, away from all outer edges. But a void in the middle changes where the center is. Now the volume of glass is trying to contract away from the edges formed by the void, as well as away from the outer edges. A much more complicated and stressfull situation. In effect a hole through the middle of a piece means that its center of contraction has become a ring.
3-d pieces with positive relief are not this complicated, but they do need more annealing time than the standard schedule given for their thickness.