Hard Rock Quarry

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SOHR - Challenge 01

Smoothing Pink Crushed Stone

In the School of Hard Rocks we seek out challenges that test patience and push perfection.  So the first challenge in 2009 is to take a bag of crushed rock from the Dollar Store and see if it can be shined up into something nice.

We started on February 27th.  I will update this page with progress snapshots as they occur. 

February 27, 2009

Starting point.  One bag of Decorative Natural Stones - crushed stone in this case.

Decorative Natural Stones from the Dollar Store
Starting point - I see some pink and some sparkle
The pink is more pronounced when wet
The entire bag - about 5 pounds

March 06, 2009

This is what the Decorative Natural Stones look like after one week in 60 - 90 grit in a 3 pound tumbler (the part on the right).  The color is more vibrant and the stones are rounding a bit - the surface is still curiously "gritty".  I added the rest of the rock and some fresh 60 - 90 grit and we will see how things turn out next time.

Today, I noticed that a lot of the grit in the barrel looked like it had just gone in.  In my larger tumblers, you don't see any grit at the end of a week - just a grey slurry.  The next tumbling run in this small barrel will be two weeks - and we will see how much grit survives that.
A little more color
Decorative Natural Stone - 1 week

March 16, 2009

I peeked in the tumbler today and found it full of thick pasty mud.  The Decorative Natural Stones are more rounded but still have a surface that feels gritty like coarse sandpaper.  There was still lots of grit that looked like it had just gone in the drum, but I changed to 120-220 grit as it was clear that continuing with 60-90 was going to generate lots of mud and some small, gritty, rounded stones.

Still more color
Decorative Natural Stones - 17 days
Maybe a finer grind will smooth this
Surface is rough at 17 days
This is the roughest surface I have encountered on tumbled stones.  They feel more "gritty" now than they did in the original bag.  I'll check in 4 or 5 days to see if there are any signs of smoothing. 

March 23, 2009

Today our Challenge rocks are smoothing and even showing a little bit more color.  The 120 - 220 grit cycle of 7 days really took the roughness from the surface and continued the rounding.  There was plenty of mud in the barrel, enough that the rocks started to stick to the sides.  The machine is running again with 500 grit silicon carbide.  We'll see if these smooth up a bit more and then we'll know the prospects of polishing.

Much smoother and a bit more color after 1 week in 120-220 grit
Decorative Natural Stones at 24 days
Might just take a polish - we'll see
Surface is smoothing after 24 days (total) and a week in 120 - 220 grit

March 30, 2009

Looks like we have a shot at getting these rocks to shine.  After a week in 500 grit, they are smooth to the touch.  The color is getting brighter.  Shrinkage has been fierce on these - they are clearly softer than most stones I tumble.  If they look nice while wet after grinding in 500 grit, we can likely get them to polish to some degree.  We'll try a week or so in 1000 grit next.

1 week in 500 grit gives us a smooth-to-touch surface and brighter color
Decorative Natural Stones after 31 days
Smooth to touch, nice color wet - I'm thinking shine-able
After 1 week in 500 grit

April 05, 2009

After a week in 1000 grit aluminum oxide, the Decorative Natural Stones feel smooth to the touch and have good color when dry.  There was a heavy froth in the barrel when I opened it, much like the froth on the top of an old malted milk.  Anyway, everything is spic and span and the rocks are back to tumbling in aluminum oxide polish. 

Smooth to the touch, good color when dry - on to polish
Decorative Natural Stones after 38 days
After 1 week in 1000 grit
Feeling smooth

April 17, 2009

We cross the finish line - and the stones do not shine - at least, not a bright shine.  They are much smaller than at the start and generally more rounded and a bit more pinkish in color and they show some hint of shine on some hard bits scattered throughout but after 49 days, I've concluded that these rocks will only grind themselves to mud if I leave them in the machine.  The last 11 days were in aluminum oxide polish with a bunch of rubber bands to cushion them - but the surface seems to be the same as after the 500 grit run.  Conclusion: this was fun but if you want smooth, shiny rocks you need to work with things like agate and quartz - and there are plenty of those stones around.

Not shiny - but done
Decorative Natural Stones - after 49 days
Even with a lot of cushion, these didn't shine
After a final 11 days in polish

Handy Tip:  Keep a very brief history of what is in a tumbler on masking tape on the tumbler lid.  I keep a notebook too, but find that the tumbler lid is really convenient.