A Blog About Stone Gathering, Tumbling and Polishing, and Rocks and Landscapes, from New Zealand – With Musical Interludes (john.tumblestone@gmail.com)
Panorama of Riverton’s Back Beach – Bluff Hill in the middle far distance, Stewart Island/Rakiura to the right, in the mist on the horizon, across Foveaux Strait
The 78 polished stones in a plastic storage container
These 78 stones were collected from the Back Beach in March 2019. They were initially tumbled in 320 grit as they were smooth beach pebbles. They were then tumbled in pre-polish and pro-polish tin oxide and burnished in borax. Altogether, these stones were processed in a 4lb rubber barrel for four weeks.
78 polished stones collected from Riverton’s Back Beach in March 2019, set out just having been dried from the opened barrel
Each stone has its own interest and attraction. The following are some of the most intriguing (Note: Some of the close-ups have been manipulated a bit to explore the patterns and colours):
The Back Beach at Riverton faces Stewart Island, some 40 kilometres away across Foveaux Strait, a rough and often treacherous stretch of water. The powerful waves are ideal for smoothing stones as they are tossed back and forth and up and down the beach.
Back Beach, Riverton, from the hill separating it from the Beach Past the Back Beach
On the Back Beach, looking back to the hill from which the previous photo was taken
The incoming wave dislodges stones, tossing them in the air and pushing them up and down and along the beach
The amount of stones on the beach varies considerably – in March 2019, a high bank of stones had been cut into in scallop shapes by the waves
The stones here are generally much smaller than the ones to be found near McCracken’s Rest, closer to the Waiau River mouth. Further up the beach, larger stones the size of your palm, can be found
For a number of years before I retired from the University of Waikato, I assisted with the supervision of Gemma Piercy-Cameron’s PhD thesis. Gemma was finally successful in completing her grand project, Baristas: The Artisan Precariat, a few months ago. Currently, Gemma is a Lecturer in Sociology and Social Policy at the University of Waikato (see her Staff Profile). I presented her with nine milestones to mark her accomplishment.
The following letter accompanied Gemma’s milestones (photos added here):
Why Nine Stones? Nine is seen to have philosophical significance, due to its unique numerical attributes. In the Hebrew tradition, for instance, Nine represents truth, since it reproduces itself when multiplied. Multiply any number by 9, then add the resulting digits and reduce them to a single digit, it always becomes a 9 again, e.g., 6 x 9 = 54, 5 + 4 = 9; 23 x 9 = 207, 2 + 0 + 7 = 9. Another attribute of Nine is that when added to any other number and then that number is reduced to a single digit, it always comes back to itself, as if nothing was added at all. For example, 5 + 9 = 14, 1 + 4 = 5; 7 + 9 = 16, 1 + 6 = 7. Nine is the Triple Triad, consisting of three times three, and so is seen as symbolic of completion, fulfillment, attainment, the beginning and the end, the ultimate whole number. Appropriate to recognise the completion of a PhD!
Stone #1 “Coffee”
Stone 1 “Coffee”
Other side of Stone 1 “Coffee”
Unknown type, collected at Riverton (Southland) July 2017, polishing completed September 2017. Polishing brought out the creamy swirl that reminded me so strongly of coffee and latte art that I knew it was destined for you.
Back Beach, Riverton, Stewart Island in background (left)
Western end of Back Beach, Riverton
Gull and stones, Back Beach, Riverton
Stone #2 “Positioned Sparkle”
Stone 2 “Positioned Sparkle”, full of quartz and large mica crystals
Same face of Stone 2 “Positioned Sparkle”
Reverse face of Stone 2 “Positioned Sparkle”
Detail of some of Stone 2’s large mica crystals
Mica-rich pegmatite rock, collected at Joyce Bay (near Charleston, Buller District) March 2017, unpolished. Your thesis reflects who you are, and sparkles as it is turned to be viewed from different positions. Different things will be seen in it depending on who views it from which position.
Joyce Bay on left – from a postcard
Source: Google Maps
Northern end of beach at Joyce Bay, where Stone 2 was found
Joyce Bay rock, full of quartz and mica
Joyce Bay, near Charleston, West Coast
Stone #3 “Effort”
Stone 3 “Effort”
Stone 3 “Effort”
Detail of Stone 3 “Effort”
Mudstone, collected at Riverton July 2017, polishing completed September 2017. This stone started millions of years ago as a number of sediment layers, being compressed by weight and heat. Your thesis consists of layers of effort and activity, building on each other, one layer being the foundation for the other. Over time, effort becomes more focused, refined, productive, until completion is reached.
Henderson Bay, Riverton
Stone #4 “Complexity”
Stone 4 “Complexity”
Detail of Stone 4 “Complexity”
Detail of Stone 4 “Complexity”
Stone 4 “Complexity”
Jasper, with silica, collected at Riverton February 2018, polishing completed August 2018. Reality is complex and resists analysis. Analysis is hard labour.
Stone #5 “Depth”
Stone 5 “Depth”
Detail of Stone 5 “Depth”
Detail of Stone 5 “Depth”
Stone 5 “Depth”
Pale green Quartzite, collected at Orepuki (Southland), April 2016, polishing completed November 2017. Depth of understanding and insight is gained by multi-method qualitative research.
The beach near Orepuki
The beach near Orepuki
Stone #6 “Found Worthy”
Stone 6 “Found Worthy”
Stone 6 “Found Worthy”
Stone 6 “Found Worthy”
Stone 6 “Found Worthy”
Stone 6 “Found Worthy”
Detail of Stone 6 “Found Worthy”
Banded Agate, collected on Birdlings Flat (Canterbury) June 2016, polishing completed September 2016. Agate is formed from quartz crystals growing in layers so small they can barely be seen. The layers build up to fill cavities in sediments left by gas bubbles in volcanic rocks. This particular banded agate is very unusual (the only one of its kind I have found) – when held up to the light, it is apparent that the bands are not smooth but have intricate and delicate lace-like waves in them. This stone will have originated in the Alps, been washed down a Canterbury river, and swept along the coast to be deposited on Birdlings Flat which abuts Banks Peninsula. Your thesis has survived close examination in the light of others’ assessments, and has been found to be worthy of scholarly esteem.
Birdlings Flat beach, the western part of Kaitorete Spit abutting Banks Peninsula
Kaitorete Spit, a 25 kms long gravel bank, looking towards Banks Peninsula, separating Lake Ellesmere from the Pacific Ocean
From the car park at Birdlings Flat
Birdlings Flat beach and Banks Peninsula
Stone #7 “Patterns”
Stone 7 “Patterns”
Detail of Stone 7 “Patterns”
Detail of Stone 7 “Patterns”
Stone 7 “Patterns”
Unknown type (possibly a type of schist?), collected at Riverton February 2018, polishing completed August 2018. Research identifies patterns and layers and makes sense of them for others.
Beach Past The Back Beach, Riverton
Beach Past The Back Beach, Riverton
Beach Past The Back Beach, Riverton
Beach Past The Back Beach, Riverton
Beach Past The Back Beach, Riverton
Beach Past The Back Beach, Riverton
Stone #8 “It takes time to construct an interesting story”
Stone 8 “It takes time to construct an interesting story”
The largest fossil worm cast in Stone 8 “It takes time to construct an interesting story”
A smaller fossil worm cast in Stone 8 “It takes time to construct an interesting story”
Detail of Stone 8 “It takes time to construct an interesting story”
Argillite, a hardened mudstone, with fossil worm casts, collected at Orepuki February 2018, polishing completed August 2018. This argillite started as mud under the sea 250-280 million years ago. The interesting linear features were left behind by ancient worms who had ingested lighter coloured mud. All pieces of scholarly writing, including your thesis, are like fossils of your thoughts at a particular period of time, persisting in existence even as you go on to other thoughts and activities.
Gemstone Beach, Orepuki
Gemstone Beach, Orepuki
Stone #9 “Well Travelled and Wide Ranging”
Stone 9 “Well Travelled and Wide Ranging”
Detail of Stone 9 “Well Travelled and Wide Ranging”
Detail of Stone 9 “Well Travelled and Wide Ranging”
Stone 9 “Well Travelled and Wide Ranging”
Quartzite, stained with iron, collected at Budleigh Salterton (Devon, England) May 2018, polishing completed August 2018. These Devon stones are identical to rocks found in Brittany in France. Some 200-250 million years ago, Brittany was mountainous and rivers drained from it northwards across the Triassic desert, across what was to become the English Channel. The quartzite rocks were tumbled into pebbles and eventually deposited as pebble beds outcropping on cliffs at the beach of Budleigh Salterton village. Good PhD research takes time, has gone places, and has a broad base of experience and reflective thought.
Just out of a 3lb borax burnishing tumble, 43 newly-polished stones from a Riverton beach.
I collected these stones at a beach I call the “Beach Past the Back Beach” at Howells Point, Riverton, in March 2019. When you reach the end of the road at Howells Point, there is a track up the sand dunes. Down the other side is this beach, which stretches for maybe 900 metres further westwards. Many of these stones were found at the far eastern corner, the area circled in this photo:
Riverton’s “Back Beach” is the stretch along the last part of the road that winds along the coast. If you walk over the dunes from there, you come to the “Beach Past the Back Beach”.
These are not particularly spectacular stones, though some are really interesting. Not all have polished perfectly, some have scratches and holes in them, but I polished them because of their intriguing colours and patterns.
Photos of a selection of these newly-polished stones:
The purpose of this and the following Posts is to examine how the 40 Riverton stones have emerged from the polishing process and to compare them with how they looked before polishing. The Seven Stages that these 40 stones have gone through are: Stage One, Stone Collection; Stage Two, Silicon Carbide 100 Grit Tumble; Stage Three, 220 Grit Tumble; Stage Four, 320 Grit Tumble; Stage Five, Tin Oxide Pre-Polish; Stage Six, Pro-Polish; and Stage Seven, Borax Burnishing.
This is the 12th Post in this series – the first Post can be found here.
To start with Stones 1 to 5 [Note: The second photo below does not do justice to the shine on the polished stones, due to the artificial lighting conditions under which the photo was taken]:
Stones 1 to 5, rough, as collectedStones 1 to 5, after polishing
STONE 1
Before polishing, Stone 1 (far left) was about 8 cms long and about 5 cms wide at its widest point (using the graph paper under it) and after polishing it has lost perhaps only a few mms of size. I had noted in Post Two of this series that Stone 1 is most likely of volcanic origin, probably rhyolite, as it has small specks in it that would have originally be gaseous pockets. [Note: I have since decided that this stone is ignimbrite, not rhyolite.] After the 100 grit tumble, these small pits were obvious. I noted after both the 220 grit tumble and 320 grit tumble that further wearing away of the stone did not do away with these pits. They would prevent the stone from achieving a smooth polish over all its surface. Further tumbling in 320 grit would not have solved this problem. I have previously (and since) tumbled the same type of stone where the gaseous pockets appear to have been filled in with material and they have been very successfully polished over all their surface.
Stone 1 has polished well except for the many gaseous pits to be found across its surface. Close inspection with my magnifying glass also revealed some small cracks that had not been worn away and which I had not previously noticed:
Stone 1 polished
Stone 1 polished
Stone 1 is covered in small pits that have not polished.
Small pits on the surface of Stone 1
In the centre of this photo, a small crack is apparent
This stone is in contrast to other rhyolites [ignimbrites] I have tumbled, where the gaseous pits have not been void:
Stone 1 is well-patterned and a nice large size. Even though it has failed to polish completely, it remains a fine specimen. The tumbling has brought out its pattern clearly.
STONE 2
Stone 2 is similar to Stone 1 in that it is of volcanic origin [probably rhyolite] and also started out with noticeable gaseous pits the size of which was actually a little larger than Stone 1. However, most of these pits were filled with material which resisted crumbling and which polished quite well. In general, Stone 2 polished much better than Stone 1. However, there are a small number of pits which did not polish and two small cracks that are apparent.
Stone 2 after polishing
Stone 2 after polishing
A pit that crumbled and did not polish
Another pit
Two cracks that had not been removed by tumbling
When rubbing a thumb across one side, a couple of these indentations are noticeable and interrupt the smoothness. Another tumble in 220 grit would probably have removed most of the pits and cracks, although there is no guarantee that all of them would have disappeared.
STONE 3
Stone 3 looks like a mudstone that has undergone metamorphic pressure. It is fine-grained and has lovely green patches and swirls. From the beginning it seemed free of pits and cracks and had polished very well. The beautiful patterns discernible in the rough stone have been revealed and clarified.
Stone 3 after polishing
Stone 3 after polishing
Close-up of a polished Stone 3
Close up of a polished Stone 3
There is just a slight roughness along one edge, not very noticeable really, but otherwise it is excellent.
STONE 4
It was noted during the inspection of Stone 4 after the 100 grit tumble that it had a small indentation in it. I would normally have tumbled it again in 100 grit, although there is always the risk that this might reveal other soft spots. After the 320 grit tumble, I saw that the indentation had smoothed out a lot and thought that it might not affect the final polish. At the end of the polishing process, Stone 4 has turned out very well.
The polished Stone 4
Stone 4 after polishing
Detal of Stone 4 after polishing
Partially smoothed out indentation
Area of partially smoothed out indentation
This stone is a breccia, composed of broken angular fragments of rock cemented together in a fine-grained matrix. Sometimes indentations in such stones are caused by a softer fragment being worn away more quickly than the rest of the stone. This is not the case here – the indentation is maybe a less compressed part of the matrix. It has polished to a significant extent but can still be felt when a thumb is rubbed over the surface of the stone. The only other notable thing is that the very edge of the point half way down the stone is slightly rough – another 320 grit tumble would have smoothed this out.
STONE 5
This stone has polished very well. It feels smooth all over. The eye can vaguely discern a few very small pits along one side which can be confirmed with a 3x magnifying glass. But these do not detract from the overall smoothness.
Stone 5 after polishing
Stone 5 after polishing
Close-up detail of Stone 5
Stone 5 looks at first glance to be a metamorphic mudstone or sandstone but closer inspection shows it to include lots of small pieces of different things, including pits (filled in) that are normally found in a volcanic stone. Many of the stones I find cannot easily be identified by me.
(This is the 11th Post in this series – the first Post can be found here.)
Steve Hart, in “Modern Rock Tumbling” (2008), attests that burnishing can make a “significant difference” in the appearance of polished stones (page 44). As one tumble-polisher has put it, “Sometimes stones are a little ‘hazy’ when they come out of the polish and small particles of polish are hidden in the tiny crevices of the stones. It helps to clean them up by burnishing the rocks in soapy water for 4-5 days.”
It was while I was doing my initial internet searches on how people tumble polished stones that I came across the idea of a post-polish burnishing tumble for up to a week using borax. Borax is sold as a white powder that dissolves easily in water. It has been used as a detergent, a food preservative (now banned for this use in some countries), an anti-fungal compound, a weed killer and a low-toxicity insecticide. It is used by tumble-polishers because it is a clean soap, lacking perfume and other additives (some use Sunlight or Ivory soap flakes instead). So I tried it and I thought that the results were great – polished stones seem to sparkle just a little more. Whether this is the case or not, I am not entirely sure, but I have the attitude that if it seems to work, why not continue it! In general, I think that a soap tumble of newly-polished stones for a day is the least that should be done, to remove polish particles and to give a final clean. My established routine practice is a tumble for around one week in one to two tablespoons of borax.[NOTE: April 2021 – I now do a borax tumble for an average of two days and the results still seem to be good.]
I polished the 40 Riverton stones, that this series is about, in borax for 10 days straight after the pro-polish tumble. This was a little longer than usual as I was busy with other things over this period. Firstly, the washed stones and pro-polish beads were replaced in the 4lb barrel, with water, and then about two tablespoons of borax were added.
Two tablespoons of borax in the 4lb barrel in which the stones and plastic beads have been placed, topped by water.
At the end of the tumble, the stones were washed then given a final weighing:
The starting weight of the unpolished stones, right before I began to work with them, was 1605 grams, the end weight is 1244 grams. This means that 361 grams were worn away during the whole polishing process, which is 22.5%, just over one-fifth, of the stone material.
SUMMARY OF TUMBLING STAGES AND TIMES (as taken from Tumbling Log)
(Stage 1 = Stone collection)
Stage 2, 100 grit = 9 days 10 1/2 hours, followed by soap tumble of 12 hours
Stage 3, 220 grit = 9 days 2 hours, followed by soap tumble of 18 hours
Stage 4, 320 grit = 9 days 19 1/2 hours, followed by soap tumble of 3 days 1 1/2 hours
Stage 5, Pre-polish = 5 days 19 hours, followed by soap tumble of 20 hours
Stage 6, Pro-polish = 14 days 5 hours
Stage 7, Borax = 10 days 2 hours
This adds up to the stones spending 49 days and 8 hours tumbling in grit and polish, with an additional 15 days and 5 1/2 hours spent tumbling in soap and borax (a total of 64 days and 13 1/2 hours). Note that this is not the minimum time needed – I often extended tumbling by a day or two in some Stages, and there were occasions where tumbling in soap went on far longer than usual. Furthermore, a smooth beach stone can usually skip Stages One and Two.
The following Posts in this series look at each of the polished stones in detail to assess the impact of this process on them. The first examines Stones 1 to 5.
NOTE: March 2021. My supplier now stocks only one grade of tin oxide polish powder instead of two. This means that Stages Five and Six can be replaced with one stage. Details can be found in UP-DATE OF “The Seven Stages in Tumble Polishing Stones” – One Less Stage. I will leave the original Posts unchanged as the detailed activities of either Stage can be applied directly to the use of one polish stage.
(This is the tenth Post in this series – the first Post can be found here. Apologies for the delay that’s interrupted this series.)
In his book, “Modern Rock Tumbling” (2013), Steve Hart, a mechanical engineer, comments that how a stone becomes shiny after polishing is both a miracle and a mystery:
There is no one who really knows what happens inside the barrel when polish is added to the rocks. The Silicon Carbide stages were relatively easy to understand, because the process was primarily mechanical erosion or abrasion. Not so with polish. There are “mysteries” that don’t add up… There are theories that a given polish may liquefy the top layers of molecules on the rocks and rearrange them so the surface is smoother. Others say it may be an acid/base pH thing, or perhaps a frictional heat buildup phenomenon which causes the rock surface to flow… Another theory is that the rock surface is simply mechanically hammered… down to a smoother condition… After really trying to understand the polish process, I had to give up, because no one… really knows what’s going on (pages 40-41).
Stage Five of tumble polishing used a “pre-polish” tin oxide powder of five micron size. Stage Six uses a “pro-polish” tin oxide powder of one micron size. In general terms, I am following the instructions provided by Colin Simmons of the Rotorua Rock and Gemstone Shop from whom I bought my tumblers. He also sells the two grades of tin oxide powder. Colin recommends that the Pro-Polish tumble should be for at least seven days, and he states that the pro-polish mixture is retainable and reusable for about six batches of tumbling as long as it does not become contaminated. In this instance, I used a pro-polish mix that I had used five times before.
The procedure for starting the Pro-Polish tumble is the same as for the Pre-Polish stage, using the key ingredients: the 4lb tumbler, the white pro-polish tin oxide powder, a plastic shaker with a tight lid, and the plastic beads kept for pro-polish tumbling (see the relevant previous Post for details):
I try to tumble a pro-polish batch for at least 10 days, even though Colin Simmons states that it is okay to tumble for only seven days (as the minimum). In this case, I had taken on a temporary job which kept me busy while the stones were tumbling and I left them for a total of 14 days and five hours before taking the barrel off the machine. The process of taking the stones out of the barrel and washing them is the same as detailed for the Pre-Polish Stage(Note, January 2022 – I have just come across an observation from an experienced polisher that using a metal colander to rinse stones at the polish stage tends to put metallic streaks on the stones. I have not noticed the same issue with a metal sieve):
I then use my pro-polish toothbrush to finish cleaning the barrel before the next stage:
However, instead of then putting the stones in a soap tumble, they undergo a longer tumble wash in borax as a burnishing process, which is Stage Seven, described in the next Post in this series.
In October (above, left), the lone figure of my friend Ray walks ahead on Gemstone Beach as I take about five steps every five minutes. I am searching for the elusive hydrogrossulars, so shiny that tumble polishing usually does not improve them. November (above, middle) also features rocks that shine but this time it’s the large mica flakes in them that sparkle. Found at Joyce Bay on the West Coast of the South Island, one such rock sits in my lounge room, beside the fire. Finally, in December (above, right), we return again to Riverton, my favourite set of beaches where I have found some of my favourite stones.
The June page for this calendar (above, left) has a photo of Kiritehere Beach, on the west coast of the North Island, which Petra and I visited in September 2018, and some of the rocks with monotis fossils that we found there. The rocks on this beach are full of these fossils. I have not tried to tumble polish them. Budleigh Salterton features on the July page (above, right). This village in Devon has a pebble beach full of red iron-stained quartzite stones from the cliffs nearby. We have visited there when we have been in Devon in the past three years. For more detail on Budleigh Salterton and its stones, see the comments on Stone #7 in the post on Twelve Stones, Part Three.
For August, one of my favourite stones appears, banded rhyolite. Stones of this type can be found on beaches along part of the south coast of the South Island, especially around Riverton and Orepuki. The beach featured on the August page is the beach past the Back Beach at Riverton (just beyond the end of the road). September’s beach is another one in the UK that Petra and I visited in 2018, Penmon Point on the Isle of Anglesey in Wales. There I found a black stone with interesting patterned fossils in it (I have not been able to identify the fossils), and a number of limestone pebbles also with fossil shells that are much fainter.
The February page (above, left) shows Birdlings Flat with Banks Peninsula in the background, along with a number of quartzite stones collected there. For March (above, right), the location is Beaumaris on the Isle of Anglesey in Wales, on the shore of Menais Strait. Next to the pier, I found three unusual stones, two of them with fossils in them. Petra and I also visited nearby Beaumaris Castle at that time.
The April page (below, left) features colourful and patterned stones from the Back Beach at Riverton, with the May page (below, right) showcasing banded agates collected at Birdlings Flat.
Every year I produce a calendar as a Christmas gift for family and friends. I use the online site DiamondPhoto to produce these. For 2019, I compiled a calendar of polished stones and locations. The following is the Cover (Gemstone Beach, Orepuki) and the January page (Henderson Bay, Riverton, with close-ups of some of the stunning stones I have found there):
Gemstone Beach, Orepuki, Southland
January calendar page: Henderson Bay, Riverton, Southland, and close-ups of polished stones found there
