This is a set of notes and comments made as I refined my technique on rock tumbling - from July thru November 2008. I was "new to the sport" so tried out many ideas that I read about on the internet. The product at the end made it all worthwhile. There are some rocks that require rework and in that sense, the process has just begun. There are new rocks in the machines now, so more notes will follow. ______________________________________________
Right now, I am getting used to tumbling. It is really interesting as you set up a batch in the machine and let it run for a week or ten days. Then you open it up, see how you did and set up for the next run. After coarse grinding, and fine grinding, and pre-polishing, and polishing and cleaning - a 5 or 6 weeks series, your rocks come out all smooth and nice.
I am just finishing a batch of rocks that I picked up in the American University parking lot. They do a pretty good job of polishing students, I thought I'd work on some of their rocks. My next run is a bunch of rocks I got from The Rock Shed in South Dakota. They will be neat.
AU Rocks rocks
Part of my next batch
To track the process, I posted before and after photos for each of the 5 phases of the tumbling run. Be patient - this will take a while.
Take 10 pounds of really cool rocks. This is actually the other half of 20 pounds of rocks I got from the Rock Shed - but you get the idea. 2.5 pounds of petrified wood, 2.5 pounds of large assorted rocks, 2.5 pounds of medium assorted rocks and 2.5 pounds of small assorted rocks. Add 1 pound of 46 - 70 grit silicon carbide - cover with water and spin for a week. 24/7
Start with this.
After one week of tumbling in 46 - 70 grit, the rocks look like this.
After 1 week in 46 - 70
One week in 46 - 70
I put them back in for an additional 14 days of tumbling in 46 - 70 grit. Initial grit loading was 1 pound - I added 8 ounces on day 8 and continuted the grind.
Muck at end of 2 week run
Rinsing off the stones after 3 weeks of grinding reveals continued smoothing of the surfaces but not as much rounding as I had hoped on the larger rocks. This batch had a wide variation of sizes. The small stones almost ground to nothing - so next time, I will work to round the larger pieces in a batch of just larger pieces.
After 3 weeks in 46 - 70 grit
3 weeks in 46 - 70
The volume of the rocks in this batch has reduced about 40%, so I am starting another batch of rough. When I get it this far along, I will sort and continue at capacity. Next pictures - probably in early September.
With one more day in September, the batches of rocks are moving along.
The 15 pounds of assorted rocks has smoothed out and is ready to move toward polishing. The volume has reduced enough so that the remaining rocks are just above half of a 15# Model B barrel. A week in 120 - 220 grit, should smooth them a bit more and then I'll check them carefully for pits and cracks and move onto polishing.
After 4 more weeks in 60-90 grit
Assorted stones - in barrel for 120-220 grit cycle
Some of the petrified wood needs a little more smoothing and the rocks from my backyard need about the same amount of work - so into a barrel and I'm in the mood for 46 - 70 for a week. Grinding is fun, and you must be patient, so I am having a great time.
Petrified wood after 7 weeks of shaping
Rocks from my backyard
While changing grit, I found that a hole had worn through the lid of my 12 pound tumbler. While I wait for the new one to come in the mail, I made a lid of plexiglass and continued grinding. This is something I sort of wanted to do but probably wouldn't have had the first lid not worn out.
Hole in A-R12 Lid - after 6 weeks
A-R12 with Plexiglass Lid
I continued grinding a mix of petrified wood, backyard stones and some red granite chunks. I am using 46 - 70 grit on this run. Here we are just getting started.
And this is what it looks like after 12 hours of grinding. The plexiglass is surprisingly smooth but the ground off residue is starting to stick. Only 6 and 1/2 more days and I can clean them up and see where we are.
The tumblers continue to roll. My batch of assorted rocks is looking pretty smooth after a week or so in 500 grit. My backyard rocks are finally shaped enough to move to finer grit and then polish.
Assorted rocks after smoothing with 500 grit
Backyard rocks after grinding w/ 46-70 grit
I had a ten day run before these next photos. Ten days with 1000 grit made the most interesting sludge. The foam was almost plastic and hard to disperse. The sludge really clung to the bucket. The rocks are looking sharp. The backyard rocks are smoothing nicely. I noticed that as the grit gets finer, the plexiglass window I am using on this tumbler is returning to clear - so you can watch the action. A fringe benefit.
Assorted rocks - after 10 days at 1000 grit
Backyard rocks after 10 days at 120-220 grit
The first batches are out. Here is what they look like. Compare this to the photo at the top of this page - before and after. The large pile at 12:00 is all smooth, shiny, polished rock. The smaller pile at 10:00 is shiny rocks with a small crack or something that I wouldn't spend time redoing. The pile at 4:00 is small, shiny, polished rocks that may end up as jewelry. The pile at 6:00 is going back for some more work. These rocks have chips or surface frosting that a little more grinding and polishing will eliminate. The last pile at 8:00 is a bunch of broken pieces that go to the voodoo pot. I am surprised by the number of broken pieces at the end of this long process. Next batch I will cull more rigorously between cycles.
Assorted Rocks Done At Last
My aim was to get a finish that looked the same wet or dry. Here is a close up photo of the stones - bone dry.
I think it is more difficult to get good pictures of the rocks than it is to polish them.
First run - polished assortment
Citrines - 20081111
The petrified wood came out smooth - at last. It took 6 weeks of grinding to get ready to polish this stuff - but it was worth the wait.
Petrified wood from my first run
Some of the backyard rocks carry a lot of cracks. This is likely caused by their exposure to freezing and thawing while laying on the surface.
Part of the objective was a surface that had the same luster wet or dry. In this photo you can see the reflection of the sky as seen through the window on the other side of the room. These rocks are bone dry, so I'll let you decide if they have the desired luster. This also explains the blue shine I picked up in some other photos.