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Posted in response to Re: Re: Re: tumbling gas from carl on August 25, 2008 at 08:33:48:

Re: Re: Re: Re: tumbling gas

Quote: i have seen, on line, a statement that this gas forming phenomenon usually occurs with glass (man made or natural (ie obsidian)) which would fit win 2 of my 3 cases)but no explanation of why was given. :End Quote

I don't know about beach glass, unless it's a naturally formed glass, but you're probably talking about man-made trash glass tumbled and worn by the ocean..

Anyway, You have to look at how the material is formed. For example: obsidian is firmed under great pressure and heat and contains a lot of microscopic gas that gets trapped during it's creation. That's why you see so many different grades of clarity of obsidian, not to mention the different minerals that cause the color variations. When you tumble obsidian, you are releasing small amounts of this high pressure gas as you erode away the material. Sometime, take a small piece of obsidian and an old heatable throwaway container and put it in a high heat source like a kiln or lab oven. Make darn sure it is a small small piece. It won't melt. It will turn to foam. This is due to the pressure and internal gasses being released by the heat. Great science experiment. What you'll have left is Tuff, a volcanic "sponge" like the ones ladies use to smooth their feet etc.

That's why you get gass when you tumble obsidian and also why some obsidian just won't ever get that really nice shine. Too much trapped gas ruins the reflection and it always looks dull, even tho the surface is polished to the same fineness as other materials.

Phil

From Phil - September 05, 2008 at 08:10:37

Message: 66954

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