surface texture of cast glass

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I am casting small (up to 10") sculptures using a 50-50 casting
plaster & silica mix and clear bullseye cullet.  I have experimented
with various schedules but it seems no matter what I do, the surface
of my pieces come out murkey and rough.  Short of polishing, what can
I do to get a smoother finish?  Would switching to a different kind of
investment improve my chances? Any suggestions would be gratefully
appreciated.
Thanks, Lisanne

Re: surface texture of cast glass
Lisanne

I think castings will always be somewhat rough looking without some form of
finishing.  We add talc powder to the investment (about 30%) which gives a
slightly finer finish.  Sandblasting the finished pieces sometimes also
improves their appearance.

Gordon

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Re: surface texture of cast glass
Thanks for the tip. Does the talc weaken your molds at all?  No
problems with flashing?  Do you use 200 or 325 mesh silica?  I've been
thinking of using a combination of 200/325 silica.  I gather you are
in Australia and maybe things are measured/ quantified differently,
but any further thoughts would be greatly appreciated.
Lisanne

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Re: surface texture of cast glass
I get good results using the ready blended investment called "glass"
made by SRS Ltd. (uk) I think they have a website.

Marcia

On 7 May 2004 11:21:19 -0700, snipped-for-privacy@sinewave.com (lisanne)
wrote:

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Re: surface texture of cast glass
Marcia wrote:
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What mold making procedure you use.
If you make a splash coat first, replace some silica with aluminium oxide.

-lauri

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