Post by scienceteacher79 on Mar 25, 2021 21:17:07 GMT -5
I love shiny black rocks, always have for some reason. I even filled three Denver Boxes with different black rocks I have tumbled, and a few I have purchased. Someday I will post pictures of them as I think they are fun even though they all look mostly black. In my quest to put in another specimen, I thought rather than putting in a raw anthracite piece of coal, I would polish it. So begins my coal saga. Since I have not seen any pictures on RTH, none for sale on Ebay and almost none on Google, I thought I would try to polish some. Buying anthracite is easy on Ebay if you can find some cheap enough and get a seller to work with you. I went to the internet and found a company in Pennsylvania where all the deep mined, hard anthracite is found. The information card is in the pictures below with the data for this coal. I went to the following: Lehigh Anthracite Sales rep was very nice and agreed to send me a large USPS box of 1-4 inch hard anthracite per my instructions. $7 for the coal and 21 for the shipping. I received 24 lbs. of hand picked pieces for me. I wanted as rounded and fracture free as possible, and he mostly obliged. Photos below are my first batch.
Step 1: Put coal in Lortone 33B rotary tumbler for 4 days. I used a handful of ceramic media and only 1 Tablespoon of 60-90 grit and filled half full with water. I checked each day. Smoothing and rounding went rather quickly but removing deep grooves and crevices was difficult. (I will do longer in my next batch to see if I can get a perfectly smooth specimen on all sides.) Sometimes chipping happens and then, the procedure begins all over again....frustrating.
Step 2: Lot-O-Tumbler filled with 40% large 5/8" smoothed ceramic media ( I despise the smaller size) and coal. I added 1 Tablespoon of 120/220 grit. This stage really removes the coal surface and after 8-10 hours, it was finished. I had to add water every couple of hours. If you let it go too long, tumbling stops from the coal dust build up at the bottom of the barrel.
Step 3: Loto with 500 Aluminum oxide and 1 tablespoon of borax for 8hrs. Much less coal dust in media and to be rinsed but still quite noticeable.
Step 4: Loto with aluminum oxide polish, media, 1 tablespoon of borax, and coal for another 8 hours. I took some out at 6 hours and did not see improvement at 8 hrs. Longer times I don't think will improve results. Hardly any coal dust in media. Mixture was light gray and rinsed off with Dawn. I use about a tablespoon and half to 3/4 cup of water to clean the coal or any rocks as this is my method. I rinse in a bucket and then again wash in an old sink after it "seems" clean over my bucket. Lot-O was used like usual with wet rocks/coal and wet media but no other water in the barrel. I misted as necessary to keep them tumbling and create a nice "paste."
The results are below.
Raw coal specimen After 4 days in the rotary tumbler finished specimen
These are the grooves chipping and crevices that are hard to get rid of. Too messy to use on my diamond blade tile saw, rotary sander works but really messy and dusty. One good thing about coal, you don't have to use water with the sander as it can take the heat build up. I would rather let it tumble longer in the rotary even though you will end up with a much smaller piece.
Picture on the left is the same specimen on the right but with harsh bright flash, right picture with subdued light which is what your eye sees unless in direct sunlight. BTW - I dremeled this piece with AO polish, water, and a polish cotton wheel and still cannot remove the micro scratches, but I am okay with that.
This concludes my experience with polishing anthracite coal. Dirty yes, but worth it to me, and quick turn around...a week from start to finish. Do babysit the Lot-O-Tumbler. Don't set it and forget it.
