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Bad suface finish kilncasting

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Bad suface finish kilncasting

Postby jagboy69 » Wed Apr 10, 2019 3:42 pm

Hello! I'm new to glass, but have been casting bronze for awhile. I am attempting to cast some chunks of glass for a current bronze piece. I am using bandust101 for investment material and microcrystalline wax. After dewax and burnout, I'm adding my glass and running my schedule. This piece is 1/2" thick and about 1inch across. I am currently fusing this at 775c for 30minutes. Funny how some areas of the glass that was in contact with the investment is nice and clear. The other 98% not so much. Could use some guidance on this one please.

Many thanks!
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Re: Bad suface finish kilncasting

Postby jagboy69 » Thu Apr 11, 2019 9:10 am

I guess I should mention, on some bad advice, this glass is 104coe rods. Obviously NOT the correct stuff for casting. :-/ It is crystal clear but the surface that contacts the mold is what has suffered.
Can anyone give me an estimate as to HOW CLEAR should be expected from glass cast in a mold?
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Re: Bad suface finish kilncasting

Postby marykaynitchie » Fri Apr 12, 2019 2:01 pm

You can expect to pick up the texture from the mold. Is it possible that the glossy bits never actually contacted the mold?

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Re: Bad suface finish kilncasting

Postby jagboy69 » Fri Apr 12, 2019 11:50 pm

Thanks Mary, Your theory makes sense it might not have touched the mold in those areas. I failed to mention I am not using a kiln wash or mold release on the investment before loading with glass. As you know, this is mixed up investment and that raises the question of when that could be done. My wax is steamed out, then the mold is placed in the kiln to dry it out slowly. To prevent cracking of the mold, I load it with glass while it's hot and get it back in the kiln.

I ran another piece last night and went really slow and gentle on the mold. The mold stayed in better condition, but the matte finish is still present in the glass. Looks like I have no choice now but to heat the glass, and torch it with an acetylene torch to flame polish, then back in the kiln for annealing. Getting proper casting glass is also on the list. Thanks for the help! If you can think of a mold release or wash that might help, I'm willing to try it. :-)

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Re: Bad suface finish kilncasting

Postby library » Thu Apr 18, 2019 12:16 pm

I fired a mold that i had air drying in my studio for 2 months (rather than two weeks) and all the white scum/ unreflective surface has gone. Additionally, if you are using coarse silica this will also affect the optical quality of the glass.
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Re: Bad suface finish kilncasting

Postby jagboy69 » Fri Apr 19, 2019 1:36 am

That's interesting... Did you dewax then put it up for 2 months or leave it with the wax in it?

I ran a fire polish schedule on the green chunk. Shame I'm losing so much texture.
I might have to look at cold working if I can't solve this soon. :cry:

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