The batch is being tumbled for the two grandchildren of one of our neighbours. The stones are mostly greywacke, which I wouldn’t normally tumble, but since these ones caught the eye of Eloise and Peter, how can I not tumble them.
On the Papatotara Coast beach (our beach out front) and also on Gemstone Beach, as well as many other beaches around New Zealand, Greywacke (pronounced Grey-wacky)is everywhere and is best described as simply a hard, grey sedimentary rock. Alternatively I have found it described as a dark hardened sandstone of fine particles of quartz, mica and feldspar cemented together.
Greywacke is so common in New Zealand it is considered by some to be our national rock! It forms most of the main mountain ranges of the South Island, well any that aren’t schist or granite and according to A Photographic Guide to Rocks & Minerals of New Zealand by Nick Mortimer, Hamish Campbell and Margaret Low, is “an important source of aggregate for concrete, for erosion protection and for building and road foundations”
Batch 58: 3lb Tumbler 4
As these stones are being tumbled for Eloise & Peter, I am going to move them all through the stages without removing any of them. Their Nana (our neighbour) will take them back to Australia for them when they are done.
Because I wouldn’t normally tumble stones like these myself, I am curious to document their journey to see how much they change (or don’t) over the different stages of grit and polish.
My prediction is that the porous-looking stones (white-ish) will polish well at all and neither will the bigger grey stone on the right of Image A.
Stage 1: F60grit
Number of Stones: 36
Weight in: 678g
2 Tbspns of F60grit
1 Tbspn Borax
No pellets added
Days Tumbling: 10
Weight out: 520g – loss of 158grams
Stage 2: 220grit
Number of Stones: 36
Weight in: 520g
2 Tbspns of 220grit
1 Tbspn Borax
Ceramic media added (added new big media)
Days Tumbling: 10
Weight out: forgot to weigh
Stage 3: 400grit
Number of Stones: 36
Weight in: 520g* (*start of Stage 2)
2 Tbspns of 400grit
1 Tbspn Borax
Ceramic media added
Days Tumbling: 7
Weight out: 378g – loss of 142grams
Batch 58: After Stage 1
Batch 58: After Stage 3
Pre-polish Soap Tumble: 2 hours in grated sunlight soap and water.
Ready to Polish
Some of the stones, especially the greywacke, have noticeably shrunk since this batch began. As a result, the barrel wasn’t quite full, so we added stones from Batch 54 (which have been patiently waiting for polish in the readies drawer) to fill it up. Interestingly, two stones from Peter & Eloise’s collection seem to have “disappeared,” leaving us with 34 stones instead of 36.
I included some stones in this batch that wouldn’t normally go through to polish because they aren’t mine, and I wanted to keep them together. I would have discarded some of the stones before the polish stage, but despite their “blemishes,” they took a shine quite well.
Stage 4: Polish Mix
Number of Stones: 34+67=103
Weight in: 378g+495g=873g
Polish Mix (2nd use): 9 Tbspns of polish mixed with 600mls of water. Plastic pellets added.
Days Tumbling: 10
Weight out: 870grams – loss of 3 grams
Borax Clean
1 Tbspn of borax with plastic pellets for cushioning for 48 hours as a final clean.
Overall I was pleased with the finished shine of the stones and I hope that Eloise and Peter like their finished tumbles! I’ve put a few extra stones into their “bag” so I hope they like those too!
Polish Complete
Batch 58 | 3lb Tumbler 4 | Papatotara Coast & Gemstone Beach (Batch54) | 20 April – 2 June 2024