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Post by 150FromFundy on Feb 24, 2009 21:50:31 GMT -5
I just finished a 2lb batch of dark amethyst from The Rock Shed. While the unblemished portions of the tumble are glass-like and reflect light, I am still getting undercutting and residual polish in the final stage. I have included some pictures and my method. I am using a twin 3lb barrel rotary tumbler (A-R2). I use a separate barrel and pellets for each stage and wash with borax between every stage. I recharge every 5 days. Before - 2lb dark amethyst  SC 60/90 - 25 days SC 120/220 + Pellets - 10 days SC 500 + Pellets - 10 days AO 1000F + Pellets - 10 days AO Polish + Pellets - 10 days Borax + Pellets - 1 day After  And some close-ups    Any recommendations would be appreciated. 150fromfundy |
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MikeS
fully equipped rock polisher
Member since January 2009
Posts: 1,081
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Post by MikeS on Feb 25, 2009 0:49:27 GMT -5
hmmm...those actually look pretty good....
Any time I do any type of quartz, I find that extra time seems to help....but I do the fine grit and polish in a vibe, not a rotory. In the vibe, I fine grit them for a week and polish them for a week using aluminium oxide. I don't use pellets, and I never burnish them after the polish stage. Every time I have burnished them after the polish, they haze up and undercut, especially smokey quartz for some reason.
Maybe try backing up to the 500 grit stage...add a little extra time for the polish and skip the final bunish...that's all I can think of....
Mike
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rallyrocks
fully equipped rock polisher
Member since November 2005
Posts: 1,507
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Post by rallyrocks on Feb 25, 2009 17:22:26 GMT -5
Undercutting refers to portions of a stone being worn away faster than adjacent portions, there is no evidence of undercutting in your pictures, and it is very unlikely to be problem with homogeneous material like amethyst.
Cracks- yeah you have a fair amount of cracking and fracturing going on, that is one of the real challenges with amethyst, its fragile stuff and highly prone to cracking- what is your "pellet to stone" ratio in stages beyond the first?
More pellets might help alleviate that problem, but even with that, some degree of cracking and fractures are pretty much going to be expected with that stuff, unless you cull out any and all pieces showing any signs of cracking at all in between each stage
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rollingstone
starting to spend too much on rocks
Member since July 2009
Posts: 236
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Post by rollingstone on Feb 25, 2009 17:29:31 GMT -5
Congratulations, that's a first-rate batch of amethyst! The rough is always terribly fractured to begin with (I think they remove it by blasting), so unless you are going to use ultra-expensive facet-grade amethyst crystals, that's as good as you'll get.
-Don
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Post by 150FromFundy on Feb 25, 2009 21:29:51 GMT -5
Thanks to all for the input! I'm new to tumbling, so maybe I was expecting too much.
I have a feeling my next logical purchase will be a vibratory tumbler for the fine grind, pre-polish and polish stages. That may not be for a while because my better half is freaking out over how much money I am spending on rocks and toys already.
By the time I get to the final stages my 3 lb rotary barrel is approximately 40% rock and 60% pellets. After the course and medium grind, it takes that many pellets to keep the barrel around the 2/3 full level.
I bought a wet tile saw after I started this load, so this rough was not trimmed before the barrel was loaded. I have another batch of amethyst and citrine (both highly fractured) that I will trim to see if the overall quality is improved.
Thanks for the encouragement and the suggestions. Each batch is getting a little better.
150fromfundy
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Post by frane on Feb 26, 2009 9:07:10 GMT -5
Hi There,
Well, I am going to add my :2cents: here.
I had the same problem with my first batch of amethyst. They chipped up in the final stage and burnish. I backed up to the 120-220 and ran for about 10 days, adding more grit but not rinsing at 5 days. Then 550 for 7-10 days and Polish for 7 days.
I added a lot of pellets to all the steps above as well as adding about 5 T of sugar to each load at the beginning. It seemed to give it enough Thickness at the beginning until a slurry could form with the new grit or polish. I suspect that is where most of the chips come from. Right at the beginning of each cycle and with the wash in between. That is why I said to add grit but not rinse when they will just need recharging of the same grit. Just pull a few out and rinse them to see progress.
When you run a rinse, leave the pellets in to coushion.
Hope that helps.
Fran
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rockerfellerz
starting to spend too much on rocks
Member since August 2008
Posts: 120
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Post by rockerfellerz on Feb 26, 2009 15:37:58 GMT -5
Looks like a pretty darn good result to me!
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darrad
fully equipped rock polisher
Member since September 2006
Posts: 1,636
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Post by darrad on Feb 26, 2009 20:29:51 GMT -5
I do not see a problem or any under rcutting. I would be quite pleased with those.
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Post by Jack ( Yorkshire) on Feb 27, 2009 3:52:04 GMT -5
A Nice batch,
Looks ok to me you should have seen my first batch !!! maybe not,
A few more pellets as rallyrocks says maybe but a nice batch well done
Jack Yorkshire uk
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