jamesp
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Post by jamesp on May 30, 2018 12:30:47 GMT -5
Sunlight on an opal can cause it to craze. Gilson created opal has no problem with heat. rockjunquie can tell you all about it. www.profoundglass.com/store/pc/viewCategories.asp?idCategory=2 Back to obsidian. varying amounts of water in layers acts like ball-bearings, creating "flow lines."  Arrowhead researchers tried to date them by the amount of breaking down, not realizing they were working with obsidian AND perlite, so they got it wrong.  I wish I was there to experience this flow Dave. Uh, from a safe distance. |
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Post by fernwood on May 30, 2018 12:39:48 GMT -5
Thanks. I have only purchased Aussie Opal in the past.
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jamesp
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Post by jamesp on May 30, 2018 12:43:19 GMT -5
The fire obsidian is probably the rarest Glass Buttes type. It is expensive and the fire lines are extremely thin. Probably not the best candidate to experiment with. I have a couple of pieces of rough that someday I will try to cut, but I'm afraid of wrecking it -- so it sits. There is an art to finding a fire layer in a piece of black obsidian with a bunch of grayish lines running through it. I'm not even sure it's worth messing around with making "doublet" blobs with glass out of it. The impurities that will be in the natural material will probably ball up the whole works on you, plus it would be easier for you to shape obsidian cabs and throw them in your tumbler to make pendant stones if you wanted to sell them. Most of the rough obsidian is not that expensive.
Agree. There are several causes to the various optical phenomena in obsidian, most all formed under high pressure conditions that will not survive in a kiln. Some Sheen types are caused by entrained gas bubbles that have been stretched into micro-fine streamers. Others also have some oriented crystals that give lens effects, and most obsidian has at least some water content (which can explode or froth up when re-heated). Fire and Fire Sheen (including some Gold Sheen) have their phenomena due to having magnetite layers stretched into nano-thin, translucent sheets that set up a thin film interference effect (TFI, the same effect that gives a thin oil slick on water its rainbow of colors, which also would very likely survive reheating. As I mentioned, obsidian forms under great pressure and heat, then cools off much more slowly than manufactured glass (which has additives that allow it to melt at lower temps and cool/anneal faster). It is not likely to be compatible to fuse alongside manufactured glass. Might be interesting to stir both obsidian and manufactured glass together, but the characteristics of the obsidian would largely be lost. I recall it being tried, along with incorporating other high-silica stones, though I don't know if anyone has documented the results. If anyone wants to experiment, I'd recommend a much slower than normal heatup and cool-down because of the trapped air and water. Thanks for these technical insights @rocks2dust. I would test tiny chips first of different OB's to lessen the excitement. I know OB has gas, tumbled it and high pressure gas bubbles certainly exist. How much air can fit into a micro bubble at possibly 500 to 1000 psi - a lot ! Respect gas under pressure. I have heated 3 chips of obsidian, 2 of the 3 ended up looking like pumice and quadrupled in size ! So respect abounds lol. Another mineral that I read about found in obsidian is felspar particles. Living in the land of kaolin and felspar this may be an additive do able in glass. Any thoughts on felspar powder ? It does crush to platelets eventually. Being into both glass and minerals I WILL be fooling around with mixing the two. Small gem grade almandines stayed together but probably had different COE, cracking the glass mildly. silicon carbide 30 grit also stayed together at 1500F in glass but severely cracked the glass, guessing large COE differences. |
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jamesp
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Post by jamesp on May 30, 2018 12:53:04 GMT -5
Thanks. I have only purchased Aussie Opal in the past. My friend used to buy Aussie and it was stored in wet clay balls. It has a thing about moisture. Thinking it may crack when it dries... Our chert down this way is made of silica precipitated out of silica rich limestone, looks killer wet, often drab when dry lest polished. Minerals that change personality when dry irritate. Or bleach in sunlight. |
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Post by MsAli on May 30, 2018 13:01:23 GMT -5
ooohhhhh those are pretty!! I will report back when I receive them. Please do. Did they say how big they are? Looks like they may be small ? |
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Post by HankRocks on May 30, 2018 13:21:31 GMT -5
jamesp You're doing great stuff with the glass and all these various combinations, so I get back to my original question from about a year ago, "When do you move on to making geodes and banded agates?"
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jamesp
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Post by jamesp on May 30, 2018 13:30:58 GMT -5
I will report back when I receive them. Please do. Did they say how big they are? Looks like they may be small ? They give the carat weight but that would confuse me not knowing such a scale. Betting smaller than we could imagine ha. |
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jamesp
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Post by jamesp on May 30, 2018 13:32:57 GMT -5
jamesp You're doing great stuff with the glass and all these various combinations, so I get back to my original question from about a year ago, "When do you move on to making geodes and banded agates?" you mean like really making them ? I wish I could make a giant sound proof geode for my wife. |
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Post by 1dave on May 30, 2018 13:35:42 GMT -5
Agate turns to opal when left in the weather over long periods.
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jamesp
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Post by jamesp on May 30, 2018 13:36:27 GMT -5
I will report back when I receive them. Please do. Did they say how big they are? Looks like they may be small ? There is an Asian section of Atlanta full of wholesale bead houses, incredible agates and stones. Some gotta be real. Aisle after aisle, cheap too. Jade opal and most of it probably synthetic. |
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jamesp
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Post by jamesp on May 30, 2018 13:36:48 GMT -5
Agate turns to opal when left in the weather over long periods. Does not. |
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Deleted
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Post by Deleted on May 30, 2018 14:11:27 GMT -5
Any thoughts on felspar powder ? It does crush to platelets eventually. Being into both glass and minerals I WILL be fooling around with mixing the two. Small gem grade almandines stayed together but probably had different COE, cracking the glass mildly. silicon carbide 30 grit also stayed together at 1500F in glass but severely cracked the glass, guessing large COE differences. Feldspar powder would probably work ok. If in doubt, I'd heat up the powder (or obsidian or other mineral) separately first to allow any water vapor or outgassing to happen, then reheat whatever survives with your glass mix. I've seen some nice effects with mica and metal leaf that gets mixed and then stretched out. Interesting about the garnet. Was it garnet sand, or a larger piece? Agree that the crazing probably due to thermal coefficient difference, though I wonder whether that might be minimized with a slower annealing phase? Used to love seeing the work done in the glass sheds when I was in school way back when - some famous people came out of that program (wish I had bought more of their work when I had the chance). |
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Post by 1dave on May 30, 2018 14:42:58 GMT -5
Agate turns to opal when left in the weather over long periods. Does not. Yes it does. I have samples.    |
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Post by hummingbirdstones on May 30, 2018 15:07:39 GMT -5
Thanks. I have only purchased Aussie Opal in the past. My friend used to buy Aussie and it was stored in wet clay balls. It has a thing about moisture. Thinking it may crack when it dries... Our chert down this way is made of silica precipitated out of silica rich limestone, looks killer wet, often drab when dry lest polished. Minerals that change personality when dry irritate. Or bleach in sunlight. I have lots of opal rough. Some is stored in water, some is not. Doesn't matter one way or another. If an opal is going to craze or crack, it will. It really all depends on the water content in the opal and the depth it was found at. When I was actively buying opal rough, there were always warnings from other cutters not to buy from certain fields because it was cracky. Other fields had extremely stable opal and you could buy it without experiencing the heartache of watching all your rough craze before your eyes. |
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Post by hummingbirdstones on May 30, 2018 15:10:26 GMT -5
Please do. Did they say how big they are? Looks like they may be small ? They give the carat weight but that would confuse me not knowing such a scale. Betting smaller than we could imagine ha. Ok, so it says 55 carats. 5 carats in a gram -- 5.5 grams total weight. Tiny.
ETA - My math sucks. 11 grams. Still tiny.
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Post by hummingbirdstones on May 30, 2018 15:14:09 GMT -5
jamesp You're doing great stuff with the glass and all these various combinations, so I get back to my original question from about a year ago, "When do you move on to making geodes and banded agates?" you mean like really making them ? I wish I could make a giant sound proof geode for my wife. <img src="//storage.proboards.com/forum/images/bbcode/video-preview.png" video="<iframe width="560" height="315" src=" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>" alt="Video Preview">
Here's a cave I bet she'd like!  |
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Post by rockpickerforever on May 30, 2018 16:42:56 GMT -5
They give the carat weight but that would confuse me not knowing such a scale. Betting smaller than we could imagine ha. Ok, so it says 55 carats. 5 carats in a gram -- 5.5 grams total weight. Tiny.
Gee, wouldn't that be 11 grams? Ya had the equation right, but the math didn't work out too good, lol.
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Post by fernwood on May 30, 2018 16:43:28 GMT -5
I agree with hummingbird. Checked my remaining stash of Aussie Opal chips. They are all about 1/4" by 1/16" thick. No cracks or deterioration. Stored in ziplock bags according to flash. Purchased in 2002. My personal necklaces made between 1988 and 2005 are fine. Rings/bracelets made in the same time frame are fine. My remaining cabs purchased in 1986 are also fine.
I have done no special climate control on any of these. Guess it all depends on quality of stones. I purchased the chips for $20.00 for 24" strand from a reputable dealer on Ebay. They even came with a guarantee. Ah, the good old days.
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jamesp
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Post by jamesp on May 30, 2018 18:38:15 GMT -5
Yes it does. I have samples. Yep, happens in these parts too. You have samples, court adjourned. Many grasses generate opaline silica, go figure "Opaline silica deposits are formed by many vascular (higher) plants. The capacity of these plants for silica absorption varies considerably according to genotype and environment. Plant communities exchange silica between soil and vegetation, especially in warmer climates. Silica deposition in epidermal cell walls offers mechanical and protective advantages. Biogenic silica particles from plants are also implicated in the causation of cancer. Recent techniques are reviewed which may aid in the identification of plant pathways for soluble silica movement to deposition sites and in the determination of ionic environments. Botanical investigations have focused on silicification of cell walls in relation to plant development, using scanning and transmission electron microscopy combined with X-ray microanalysis. Silica deposition in macrohair walls of the lemma of canary grass (Phalaris) " |
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jamesp
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Post by jamesp on May 30, 2018 18:49:56 GMT -5
you mean like really making them ? I wish I could make a giant sound proof geode for my wife. <img src="//storage.proboards.com/forum/images/bbcode/video-preview.png" video="<iframe width="560" height="315" src=" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>" alt="Video Preview">
Here's a cave I bet she'd like! Lol, a lady cave. I had more devious intentions  . THAT is a big geode. |
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. THAT is a big geode.
