|
|
Post by Dilly Dally & Wife on Jun 24, 2008 21:11:54 GMT -5
Hi, I'm Fran. I'm trying to tumble larger pieces of obsidian (2- inches +) and I've gone through the first 2 stages of the grit and they are coming out white. Does anyone have any advise as to what we are doing wrong ?
|
|
Sabre52
Cave Dweller 
Me and my gal, Rosie
Member since August 2005
Posts: 20,494
|
Post by Sabre52 on Jun 24, 2008 22:58:22 GMT -5
Howdy Fran, Obsidian is actually kind of fragile and tends to frost or craze when the hunks knock together during the tumble, especially when you do larger pieces. Try using ceramic media or smaller bits of obsidian to cushion the load. You can also use plastic pellets but that does slow the grind a bit. Also, if you reuse old slurry, you can thicken the slurry and make the stones less likely to pound each other as hard. Main thing is , you want to have the stones slide against each other, not knock against each other and plastic pellets are a must for the fine grind-polish stages. Also, if you check the RTH home page samples section, I think Banjo has an excellent tutorial on polishing obsidian..Mel
|
|
|
|
Post by deb193redux on Jun 24, 2008 23:05:37 GMT -5
Is the barrel big enough for these larger pieces? What size barrel? How full was it?
|
|
rollingstone
starting to spend too much on rocks
Member since July 2009
Posts: 236
|
Post by rollingstone on Jun 25, 2008 1:41:39 GMT -5
I found that with obsidian in a 6 lb rotary tumbler, any piece of rough bigger than 35 grams (about 1.5 ounces) was a waste of time. It would chip no matter how I tried to cushion the load, and would also chip a bunch of the smaller obsidian pieces that were in the barrel with it. Obsidian looks for any excuse to chip and frost along the edges. Smaller is better.
-Don
|
|
|
|
Post by connrock on Jun 25, 2008 8:20:01 GMT -5
No matter what material you're tumbling you MUST have a mixed size load with at LEAST 1/3 being about 1/2".
This not only helps the load to not clash but also gives you the necessary "surface" contact between each rock which creates the "true" tumbling action in the barrel.
In order to tumble several pieces 1.5" - 2" (of any material) you MUST have a very big barrel in order to get the proper "mixture" of different size rocks and or ceramic media.
If you do have a large tumbler the amount of ceramic media can be a bit expensive.Another thing you may want to try for a "filler/cushion" is ordinary broken glass.
I also use "pea gravel" here in CT as it has a lot of mica and other soft materials in it.This creates a fast slurry which not only cushions the load,gives a LOT of surface contact but also slows the "action" down in the barrel.
Pea gravel WILL vary in it's composition in different areas of the country and world so be careful to not use any that is of a hard consistency as it will cause more problems then you have now! LOL
Good luck and keep us "posted"!
connrock
|
|
