[ATM] Microwave heating of glass

[Ian Williams <i.r.williams@bristol.ac.uk>]

Now before you all jump up and down and say glass is an insulator with 
very low microwave absorption (as stated previously on these lists), you 
might want to look at this rather daring website showing how to melt  
glass with a home microwave oven:

http://tiny.cc/meltglass

I'm aware that with the method demonstrated on that website, this is 
potentially a very hazardous thing to try, but then I know that looking 
at the sun with a telescope is hazardous too, and that amateur furnace 
making can be dangerous.  Its all in the method.

It seems possible to make a small scale glass furnace using a microwave 
oven with the assumption that the glass is heated to 'cherry-red' 
temperatures first.  Once hot enough, the relative permittivity of the 
glass increases and the glass starts to absorb the microwaves.  If the 
rate of the microwave heating can be controlled and the heating 
performed evenly enough, the glass can be made molten.

So, does the following sound at all feasible and if not how might the 
problems be overcome?: 
* Set-up a microwave-oven outside in an open space, preferably behind 
some safety screens (not in the kitchen my wife says!).
* Break pyrex up into small pieces and place pieces into a ceramic 
crucible or appropriate refactory container.
* Heat glass using a blow torch until contents are as evenly hot as 
possible. 
* Place glass into said oven and heat at an initially low power for a 
set time. Later, increase power setting if it was insufficient.  Or 
better still, arrange for remote control of the power setting and relate 
this to the temperature of the glass as read by a light-emmision 
thermometer.

The heating leads to 'microwave stirring' of the glass once its molten 
which is a benefit.  I suspect the difficulty would be in controlling 
the temperature of the melt as it cools.  Uneven heating may be a 
problem too - the microwave would need to be one of the microwave 
stirrer types.

So is this a route to an amateur glass furnace?

Thanks for humouring me,
Kind regards,
Ian Williams.
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