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Post by grumpybill on May 24, 2018 11:54:32 GMT -5
Finished up my 1st ever batch of glass and obsidian a few weeks ago. The glass is cullet from a long gone local plant. The obsidian came from various sources. Shaping was done on a 10" tile saw, followed by course grind in a rotary barrel. Subsequent stages were done in a Lot-O. I used AO polish that came with a used tumbler and I suspect it was old-school 1200 polish because there was little (if any) change after the 1000 stage. A few of the finished pieces:
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Post by mohs on May 24, 2018 12:22:53 GMT -5
that is a fine project of shine you have going on !
are the black ob's translucent?
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Post by grumpybill on May 24, 2018 12:44:04 GMT -5
are the black ob's translucent? Nope. But the black areas of the mahogany are.
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jamesp
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Member since October 2012
Posts: 36,561
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Post by jamesp on May 24, 2018 12:55:19 GMT -5
Looking great grumpybill.
Is all the glass slag glass from the old operation ?
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Post by fernwood on May 24, 2018 12:59:54 GMT -5
Very nice looking.
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Post by grumpybill on May 24, 2018 13:52:00 GMT -5
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Post by MsAli on May 24, 2018 15:09:57 GMT -5
Those are great!
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saxplayer
fully equipped rock polisher
Member since March 2018
Posts: 1,327
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Post by saxplayer on May 24, 2018 15:15:14 GMT -5
Nicely done!
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timloco
has rocks in the head
Member since April 2012
Posts: 545
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Post by timloco on May 24, 2018 15:18:19 GMT -5
those turned out great!
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Post by grumpybill on May 24, 2018 15:47:07 GMT -5
Thanks for the compliments, everyone, but I'm not really happy with the "shine". Hopefully one of the other generic AO polishes I have on hand will do a better job on the next batch. If all else fails I'll break down and buy some new polish.
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jamesp
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Member since October 2012
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Post by jamesp on May 24, 2018 16:49:35 GMT -5
Send me some of that slag and I will see what it does in the kiln.
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Post by grumpybill on May 24, 2018 16:57:42 GMT -5
Send me some of that slag and I will see what it does in the kiln. Shoot me your address. I'll send some of the "banded" slag and a variety of the colored plate glass that was intended for refrigerator shelves in the 40s and 50s.
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jamesp
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Member since October 2012
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Post by jamesp on May 25, 2018 4:41:52 GMT -5
They may have used Pyrex/borosilicate for refrigerator shelves since it takes sharp temperature changes and scratches less. I believe it is normally a harder glass and requires higher temps, it expands less when cold/hot.
Obsidian is usually softer than the soda glass I tinker with, mahogany seems to be harder than the other obsidians. Most opaque glass is referred to as slag glass in vase lingo and it seems to be delicate in many cases because it might be a broad mix of different glass. Different glass has varied coefficients of expansion and likes to set up cracks when cooled down.
A glass blower can compare the coefficient of expansion of 2 different glasses by stretching a say 2 foot strand of each glass and attaching them together. If the 2 strands are straight after cooling then they have the same COE, if they curve after cooling they are not compatible.
Dang it, I frosted the edges of a load of glass for the first time in a long time in the Vibrasonic. Will have to re-run in the rotary in AO 500 or possibly SiC 500 depending on how deep the damage is.
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Post by grumpybill on May 25, 2018 5:37:43 GMT -5
I agree with your comments about hardness, jamesp. The flat glass with a slight texture, which I think was fridge shelving, is much harder than obsidian and the red ashtray I tumbled with it. Took twice as long in the course run. The softest I've found to be the crystal clear chunks, although they polish up well. Also agree about black vs mahogany obsidian. Noticeable even while sawing. The hardest slag I've found so far are some opaque light/lime green chunks that (other than the color) look like a cross between a wad of chewing gum and an apple fritter. Breaks apart at the folds/seams when sawing and takes forever in the barrel. I'm not going to bother with any more of it. The slag with bands, like two in the photos above, is fairly soft but is a bitch to work with. Comes apart at the seams both while sawing and in every stage of tumbling. Also, it may not be suitable for your kilns...lots a little bubbles that might not melt out. They add "character" to my pendants, though. I assume the main ingredients of the old style pale green glass were sand and lime because I find a lot of the slag stuck to what looks like sand-cement masonry grout. At first I though it had spilt onto sandstone. Interestingly, I have a piece of that sandstone-looking stuff with a foil-thin coating of copper on it. Is/was copper used as a coloring agent in glass?
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jamesp
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Member since October 2012
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Post by jamesp on May 25, 2018 7:52:32 GMT -5
Glass variable. No doubt about it. Mohs 4.5 to 6.5.
Melting almost always improves bubbles by letting the bubbles rise and exit.
Tumbling is a great test of strength. Some glass breaks, usually because COE problems. Some is darn tough and hard to break. Yellow red and orange glass seems to be vulnerable to fractures, may be iron not sure.
Lots of metals used as color]ing agents, search internet, lots written about it.
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Fossilman
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Member since January 2009
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Post by Fossilman on May 25, 2018 9:36:44 GMT -5
Awesome rolls my friend....... Might have to invest in a "Vibe"..... That glass rolls pretty nice, liking the colors!
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