janec
off to a rocking start
Member since December 2014
Posts: 2 
|
Post by janec on Dec 27, 2014 13:57:05 GMT -5
This is my first post here. My husband gave me a tumbler for Christmas to polish the Petoskeys I collected last summer. I read in one post that Petoskeys are soft, so I'm not sure where to start with my polishing project. I collected them on the shore of Lake Michigan, and they feel very smooth already. Any tips will be greatly appreciated!
|
|
|
|
Post by jakesrocks on Dec 27, 2014 14:10:56 GMT -5
Welcome aboard janec.
I'm not an expert on Petoskeys, but I think I would start with 220 grit and lots of plastic pellet filler. Check your rocks every couple of days. When all pits are removed clean everything real good and move on to the next grit stage. Use fresh plastic pellets with each grit change.
Petoskeys won't take a mirror shine, but will take a nice shine. Good luck, and post pics of your progress.
|
|
|
|
Post by Jugglerguy on Dec 27, 2014 14:16:38 GMT -5
Welcome to the site, Jane. I hate to tell you this, but you can't tumble Petoskey stones. At least everything I've read says that you can't. I live in Alpena, so my son and I have polished a lot of Petoskey stones, but never in a tumbler. We use a machine called a flat lap, which is a grinder that spins a flat, horizontal disk of sand paper while water drips on it to keep it cool and lubricated. Each stone is done by hand.
I have used my tumblers to rough grind Petoskeys just to sort out the good ones from the bad ones and to do some initial grinding. To do this, I used 1 tablespoon of coarse grit (60/90 or 80 grit) in a six pound barrel. I checked on my stones after about 3 days because they're so soft. I also used way more water than I usually use. I think I used a cup and a half or maybe two cups. If you don't use a lot of water, the slurry gets thick like pudding after only a couple days.
So after the initial tumble, I use a coarse disc on my flat lap and grind all the surfaces until there are no concave parts left. Then I continue on to finer and finer grits. The grits I use are 60, 120, 220, 600, and 1200. You can use either silicon carbide or diamond, but diamond is not necessary. Then I use a paste called Zam on a felt Dremel wheel for the final polish.
In between grits, I dry the rock off with a fan and check for spots I missed. It's a lot easier to see the missed spots when the stone is dry.
If you want more details, I would be glad to help you out.
|
|
|
|
Post by Jugglerguy on Dec 27, 2014 14:18:13 GMT -5
I forgot to mention that you can do all of the above by hand with silicon carbide wet/dry sandpaper too. You can use a file for the first step if there are really bad spots. It will take a whole lot longer though.
My son's Petoskey stones:
Don't give up on your tumbler. There are lots of other beach rocks from Lake Michigan that you can tumble.
|
|
janec
off to a rocking start
Member since December 2014
Posts: 2
|
Post by janec on Dec 28, 2014 14:52:28 GMT -5
Thank you, Don and Rob, for you advise. I should have done more research on how to polish Petoskey stones before putting tumbler on my Christmas list... Well, I will definitely use my tumbler to polish all the other stones I have accumulated. My Petoskey stones will have to wait. I have roughly 100 of them.
Rob, your son has quite a collection of Petoskey and other stones!
Jane
|
|
|
|
Post by Jugglerguy on Dec 28, 2014 15:56:10 GMT -5
Stick around, Jane, there's lots to learn here. There are some excellent tumblers who can give you all the advice you'll ever need.
|
|
Deleted
Deleted Member
Member since January 1970
Posts: 0
|
Post by Deleted on Dec 30, 2014 13:55:55 GMT -5
Thank you, Don and Rob, for you advise. I should have done more research on how to polish Petoskey stones before putting tumbler on my Christmas list... Well, I will definitely use my tumbler to polish all the other stones I have accumulated. My Petoskey stones will have to wait. I have roughly 100 of them. Rob, your son has quite a collection of Petoskey and other stones! Jane Lake Michigan can keep you busy tumbling for a lifetime!! This is a great website with a bunch of awesome folks. You've already experienced a bit of that! Welcome and Happy New Year!! |
|
|
|
Post by captbob on Dec 30, 2014 14:02:53 GMT -5
|
|
|
|
Post by pghram on Dec 31, 2014 12:44:23 GMT -5
Welcome to the forum.
Rich
|
|
