You be might think of a portal to the Nether, or Dragon Glass to combat White Walkers. Whichever it is, obsidian is mysterious, beautiful, and difficult to tumble.
Volcanic Glass
Obsidian is an igneous stone formed from from rapidly cooled felsic (rich in feldspar and quartz) lava. It looks similar black or dark green glass, and has been used for centuries to make knife points arrowheads because it has no crystal structure, and can be easily chipped and shaped without cracking.
There are several types of this stone, including snowflake and rainbow obsidian. The rainbow variety has a mysterious iridescence caused by the presence of microscopic rods of hedenbergite crystal. I purchased these pieces from Rough Stone Rocks online specifically for the purpose of tumbling.
Let’s Get Ready To Tumble
This unique stone is relatively difficult to tumble, because like glass, it is fragile. These rocks are prone to chipping and breaking in a rock tumbler, so it is important to use tumbling media to cushion the rocks.
Obsidian is a relatively soft rock compared to minerals like quartz, meaning that it is best not to tumble obsidian with other types of rocks in the same barrel. It also means that these stones don’t need as much time to tumble.
I added 1lb of obsidian to my 3lb Chicago Electric twin barrel tumbler, and I filled the extra space with Polly Plastics tumbling pellets; ensuring that the tumbler barrel was 2/3 full by volume.
I was very eager to tumble these stones because I wanted to see if they really had a rainbow shine. I hastily started the rocks in stage 1 without doing much prior research, but after about day 3 I started to wonder if I had made a mistake.
I read past experiences from other folks who tumbled obsidian and many accounts included just skipping stage 1 altogether and jumping right to stage 2.
I began to panic and pulled my rocks out at the end of day 3, which was several days earlier than I had intended. I figured that since most people skip stage 1, I should just skip now to stage 3 to avoid over-tumbling these fragile stones.
I decided run the stage 3 cycle for a longer time since I had completely skipped stage 2. I was also out of town during the stage 3 tumble, and my trip got extended several days resulting in an extra long tumble.
Something about this seemed familiar… (see My First Tumble). I moved the stones into the final polish stage even though something in the back of my mind was saying that this is not right.
Final Results
I realized at the end that I made a big mistake by skipping stage 2. I have never found success by skipping stages, but to be fair I also have never tumbled anything as soft as obsidian before. Either way, my stones were dull; even after a burnish cycle.
To make things even worse, the stones tumbled for plenty of total time, but not enough time in the proper stages. This meant that the rocks were subjected to a lot of contact, which created nicks and cracks on the surfaces.
I immediately knew that I would have to start over with these. The best thing I could do was to start over at stage 2 and try again, and wonder if I even learned anything from my first tumble.
Tumbling Recipe
- Tumbler: Chicago Electric Dual Drum Rotary Rock Tumbler
- Grit: Tomnp tumbler grit from A
- Media: Polly Plastics Pellets
- Stones: Rainbow Obsidian from Rough Stone Rocks
- Ivory soap and Borax for washing and burnishing
| Grit | Time |
| #1 Silicon Carbide 60 – 2 tbs | 3 days |
| Ivory soap wash | 1 day |
| #3 Silicon Carbide 500 – 2tbs | 14 days |
| Ivory soap wash | 1 day |
| #4 Aluminum Oxide 1200 Polish – 2 tbs | 5 days |
| Borax and Ivory soap burnish | 1 day |
I was not happy with these results, and recommend skipping stage 1 altogether and doing a 8-12 day tumble in grit 2 to start instead.