Sustainable Rock Tumbling
Turning Art Carbon Neutral
By Rachel Elias
At the start of my inquiry, I had not ever used a rock tumbler. I had done some
lapidary work and had lots of agates that I collected from Southwest Washington. I had
just started the Rock and Gem club and inherited the student account from the previous
geology club and the Lortorne rock tumbler they bought. I know it was hardly used
because in the box, they included a note that said the motor ran hot so they stopped using
it and thought it was broken.
I got the idea to make a solar powered rock tumbler from viewing one YouTube video.
And the idea for home made ones to put in a river from another YouTube video. I thought
it looked simple and doable.
But I needed to start at square one: learning how to use a rock tumbler.
There is a lack of instruction on how to tumble rocks because it is an art form.
There are a few blog entries and YouTube videos (if you want to sit through someone
talking for fifteen minutes). But most of the help I got was through experience because
the information out there got me started but could not cover all the bumps in the road. I
had to learn by doing and get a feel for the art of rock tumbling. And I also received lots
of help from Facebook groups, filled with people who have been tumbling rocks for a
long time.
So I created a rock tumbling guide meant to stay with the club’s rock tumbler and
teach future club members how to tumble. In this report, I will bring up concepts from
what I learned as they are relevant to the development of my project. The manual is
attached at the end of this report.
I would not describe rock tumbling as environmentally friendly. It must be
plugged in at all times, and it takes at least a month to polish rocks, usually more. The
grit cannot be poured down the drain because it will clog it. It must be disposed of on
gravel or cement, because it is similar to cement when it dries. One must add small
plastic pellets (which are horrible for the environment and can end up in the ocean) for
cushioning (other sources can be used such as crushed walnut shells, but pellets work the
best).
So you get what we have here, people trying to use their favorite hobbies and art
as a way to also promote environmental stewardship. “turning art carbon neutral” and you
also get polished rocks 
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The Sustainable rock tumbling group wants to figure out ways to polish agates,
jaspers and petrified wood found locally, with renewable energy.
The teammates are Rachel and Antonio.
Rachel is looking into solar array calculations and pricing and learning how to
tumble rocks successfully. Antonio joined the project mid way through the quarter and is
looking into materials for a homemade tumbler to put in the river and coming up with
designs.
Our research project connects to power, education and sustainable art.
There are three main aspects of the project. They are:
• The Solar powered rock tumbler
• The Hydropower homemade rock tumbler
• The educational component with community outreach and the Rock and Gem club and
Rock tumbling in general.
If it works, the solar powered rock tumbler will be a permanent instillation at
evergreen, managed by the rock and gem club. It would serve as an educational tool for
learning about solar panels, rock tumbling and a place for people to get their stones
polished, even if they don’t want to learn how to tumble themselves. Just by word of
mouth, the rock and gem club has tumbled rocks collected by 6 different people in the
evergreen community. I only expect this to grow with the onset of a solar powered
tumbler.
Another potential for this is traveling to local schools and teaching kids about
their local geology and tumbling. Possibly taking them out to a river to hunt for agates
and then tumbling a rock from each student while they also learn about solar power!
The evolution of my project:
In the beginning, I thought the solar power would be great and the tumbler could
stop tumbling at night and pick back up in the day. I learned this to not be the case when I
unplugged the tumbler for a night and the next day, the grit settled into cement and
trapped the rocks. I then steered away from the solar power because I needed a constant
supply of energy and I did not want to plug it in at night, or have to release the rocks
from the cement every single day.
I turned my focus then to the river-powered tumbler because evergreen has a
freshwater spring that is always bubbling and flowing. I could put it there. I wanted to use
recycled materials so I began in places like the bike shop and goodwill and trash cans to
start making it. We did end up making one with a coffee tin; super glued old cassette tape
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cases as the “wings” and a lamp post to stick into the clay. This one fell apart after three
days because it became waterlogged. The design has to be tightly sealed at the holes yet
lose enough to spin on its axis. I’m still perplexed by this.
So then I thought of making two waterwheels from old bicycle wheels. One that
turns by spoons moving through the water and the other one attached to it that has sealed
peanut butter jars with the rocks and grit inside them. That way it could be out of the
river. And then I considered that cleaning and releasing the grit (silicon carbide) and fine
polish particulates (Aluminum oxide) into the environment might not be so great. And a
weekly cleaning might be a large chore.
I learned this at the very end of the quarter that I can run coarse 60/90 silicon
carbide grit for around 3 months and then go straight to polish, skipping 2 steps and only
having to clean it once. This is because the grit breaks down into ever smaller yet still
angular particles. This is significant because if I can design one to go in the river, I don’t
have to clean it every week like traditional tumbling. If the tumbler is sealed and turns
well, I can leave it there with no worries because the site by the freshwater spring
remains a constant flow. Not too strong or too weak!
Before I had learned that, I turned my energy back to the solar powered idea,
allowing it to be plugged into the grid. Even though I can’t make it run totally off solar,
the educational components are valuable and I can still save half the energy and carbon
costs. (See later for calculations). It was also valuable to learn how solar panels work, and
doing the research behind that. Even if I wasn’t going to install the array, I wanted to
develop a plan for potential future installations and spin offs from this project.
Then Antonio joined my project and we decided that I would focus on the solar
plan and he would on the river design.
Hypotheses:
•The water wheel is a successful design and grit and polish are not harmful to dispose of
in the environment. Rocks are polished in 4 weeks.
- Rocks polished in 3 months
•The water wheel works but cleaning it is difficult outdoors because grit and polish are
harmful to the ecosystem (fish, bugs and birds) and are so small that they never go away.
So cleaning is a chore and makes it impractical.
•The evergreen stream does not get enough water flow to power the tumbler.
•The bank is not sturdy enough to support the wheel without causing erosion.
•This is a great learning project for kids to do with their parents.
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•There is enough sun in Olympia in a location that is also close to a grid plug in.
•There just isn’t enough sun here for this idea to work and create an impact.
•There is almost no interest in rock tumbling at Evergreen
Related to power,
The Loritone 3A tumbler motor is 115 AC 60 HZ .57 amps and 36 Watts (AC). I would
need a voltage regulator that will deliver the necessary power to the tumbler in the
summer and then at night have power from the grid. When the panels are generating more
than enough electricity, they will feed power into the grid
A big question that my project addresses is, can power from solar energy be predictable?
(And all renewable energy sources for that matter). And how do we deal with solar power
in the dark and clouds?
This brings us to think about power in a way that is governed by natural forces. It forces
us to work with the elements instead of building a system that allows us to have all the
power we want when we want it.
Since the rock tumbler must be turning all the time, figuring out how to power it with
solar is a great way to test these questions. Battery technology, correct placement of
panels and extra solar space to prepare for cloudy days are essential.
But having a grid plug in back up is needed. The tumbler is in a way a metaphor for
modern life. We need a reliable grid for power at all hours.
I need to find out if the motor will turn slower if receiving less than 36 watts, or if it
won’t turn at all unless its getting 36 watts.
Based on my observations at the library roof solar panels, I saw that they were receiving
1/9th of the power on a cloudy day. (Yes cloudy has a spectrum. This was the kind of
cloudy where I could see the sun - as if it were a planet - through the clouds).
The cost of energy in running my rock tumbler in Washington state is $ 2.24
@ 8.66 cents per kilowatt hour
30 days x 24 hours = 720 hours
720hours x 36 watts = 25920/1000 = 25.92 kwh
25.92 kWh • $ 0.0866 = $ 2.244672 dollars per load of rocks in my tumbler
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The cost of energy in running my rock tumbler in Hawaii is $ 9.09
@ 35 cents per kwh
25.92 kwh • $ 0.3506 = $ 9.087552 dollars per load of rocks in my tumbler!
The difference is staggering. And wouldn't we expect the price to only go up with
foreseeable shortages of cheap energy? For someone tumbling rocks their whole life and
living in Hawaii, this can add up. (But since there are no agates in Hawaii, not many
people tumble rocks as a hobby. While, the PNW is one of the hotspots in the country for
lapidary work).
The natural art and treasure that stones are, is enhanced by shaping and polishing them.
This project is a quest to find ways of sustainably doing so.
In my last post, I described the power saving and educational tool that the solar power
rock tumbler could be. This is an analysis of the solar power relationship.
How many solar panels are needed to run the tumbler in the winter?
Pout = E • N • A • S = EA’S
Explained:
Excluding charging the battery for night time operation, the wattage desired to run the
tumbler (rounded to 40watts) requires an area of panels described as the panel Efficiency
(10%) times the Number of solar panels times the Area (N and A can be combined) times
the Solar energy (watts per meters squared).
As Olympia’s averages calculate, the power from the sun (S) is 100w/m2 in the winter.
As I observed on the panels on the roof of the library, on a cloudy winter day they were
generating 1/10th of their max power.
So to calculate solar panel area needed for the darkest rainiest day in Olympia, The solar
energy becomes 10watts per square meter.
P = EAS
P/ES = A
40/0.10 • 10 w/m2 = A = 400/10 = 40m2
Daaaaang. That’s a huge set up!
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So, how about I don’t run the solar tumbler in the winter and just do it in the summer?
How much area of solar panels would I need?
40/10= 4 • 40/.1 = 40 •10 = 400 / 100 = A = 4m2
To run a 40 watt tumbler in sunny months in Olympia, it requires four meters square area
of solar panels.
The Carbon Savings:
Because the tumbler will be running from the grid at night, we can expect carbon
emissions to be cut in half.
WA electricity = 0.83CO2lb/KWh
720 hrs x 36W (0.036KW) = 25920/1000 = 26KWh = 21.51lbs CO2 / batch of rocks
tumbled the traditional way.
Solar power tumbled for one month = 10.75 lbCO2 / batch of rocks.
Traditional:
215 lbs / year
2,150 lbs/ 10yr
Solar:
107 lbs / year
1,075 lbs / 10yr
Conclusion:
I have led several rock hunting trips with the rock and gem club. Based on
members’ reactions, I see that teaching rock hounding is important to people here. It gets
them thinking about common things around them every day in a refreshing new and
inspired way. It’s a great way to slow down and observe closely the environment around
you. And it is really, finding treasure!
I think that my plans have shown that the solar powered rock tumbler can be cost
effective. As it is a long term installation, there is potential for money savings as well as
the value generated by the polished rocks that can be sold or even turned into jewelry. It
is a great way for people to get excited about art, nature, our local environment and solar
power.
The rock club will continue to play with home made designs and is excited about
the future of it all.
Rock tumbler info:
http://www.chemguide.co.uk/inorganic/period3/oxidesh2o.html
http://www.makeitfrom.com/material-properties/Alumina-Aluminum-Oxide-Al2O3/
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http://rocktumbler.com/polish.shtml
http://rocktumbler.com/blog/
http://rocktumbler.com/blog/what-is-silicon-carbide-grit/
http://rocktumbler.com/tips/rock-tumbler-instructions/
http://rocktumbler.com/tips/rock-tumbler-cost/
http://silgro.com/RockTumbling.htm
Solar calculations:
http://www.rapidtables.com/calc/electric/watt-to-kwh-calculator.htm
http://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_5_6_a
picture
http://awesci.com/wp-content/uploads/2014/03/Dunning-Kruger.jpg
http://www.ceramicmaterials.saint-gobain.com/landingimg.aspx?id=243802
http://www.microspheresnanospheres.com/Microspheres/Inorganic/Alumina/Al2O3%20carboxyl.htm