A Blog About Stone Gathering, Tumbling and Polishing, and Rocks and Landscapes, from New Zealand – With Musical Interludes (john.tumblestone@gmail.com)
(This is the ninth Post in this series – the first Post can be found here.)
Two of the stones have suffered some minor damage in the Pre-Polish tumble, probably from bumping into other stones. This is despite careful handling and the use of plastic beads to cushion collisions in the barrel. This will happen from time to time due to the brittle make-up of some stones. Stone 6 has lost a small chip in its side:
Stone 12 has has lost three or four small pieces, the largest being apparent in the photo below:
In such cases, stones are usually returned to Stage Two or Three, to be re-tumbled with 220 or 320 grit to get rid of the pits. However, I will put them through to the Pro-Polish stage for the sake of this series of Posts.
The following are the stones as they looked upon initial collection from the beach at Riverton and then upon completion of Stage Five, Pre-Polish. In both instances, the stones are dry. Note that the same sized segment of graph paper is provided in these comparative photos. At present the stones look a lot smoother and shinier, and are slightly smaller. Their colours are clearer and brighter, with any patterns being more obvious.
Stones 1 to 5:
Stones 6 to 10:
The grain of Stone 6 is now apparent. The wearing away of Stone 7 has led to the band across its lower part to be uncovered more and thus made to appear larger.
Stones 11 to 15:
Stone 12 now has a depth to it as parts of it are translucent.
Stones 16 to 20:
Stones 21 to 25:
Stones 26 to 30:
Stones 31 to 35:
Stones 36 to 40:
The next step is Stage Six, the Pro-Polish tumble.
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 eighth Post in this series – the first Post can be found here.)
Stages Two, Three and Four tumble the stones in different grades of silicon carbide grit, shaping and smoothing them, ready for the two polishing stages. I use two different grades of tin oxide for my polishing – others use a very fine silicon carbide grit (e.g., 600 grade), sometimes skipping the 320 grit tumble stage, followed by only one polish-tumble with a powder such as tin oxide, aluminium oxide, cerium oxide, or chrome oxide.
I am following the stages set down in the Instructions provided by Colin Simmons of the Rotorua Rock and Gemstone Shop when I bought my tumblers. He also sells tin oxide powder, which is why I use it – it is the cheapest polish powder. The “Pre-Polish” stage uses powder of a five micron size while the “Pro-Polish” stage uses powder of one micron size. “Pre” and “Pro” look very similar so you have to be extra careful when labelling containers, sieves, beads etc. and when using them.
Colin Simmons recommends that the Pre-Polish tumble should be for three to five days, which is shorter than the other tumble stages (which should be for at least seven days), and he states that the pre-polish mixture is retainable and reusable for about six batches of tumbling as long as it does not become contaminated.
Stage Five begins with gathering together the key ingredients: the 4lb tumbler, the white pre-polish tin oxide powder, a plastic shaker with a tight lid, and the plastic beads kept for the pre-polish tumbling:
The 40 stones are then carefully placed into the barrel – care is taken to avoid chipping them. After the first layer of stones, I add a layer of plastic beads, just to make sure the stones are cushioned from the outset when tumbling starts:
Adding some plastic beads after the first layer of stones in the barrel.
After all the stones are in the barrel, I use plastic beads to fill the barrel up to about the two-thirds level (more beads are needed at this than at earlier stages as the stones are now smaller than when they started):
The barrel two-thirds full with stones and beads.
The next job is to add the pre-polish mixture. Often a previously used mix will be available. In this case, I created a new mix from the start. Following Colin Simmons’ Instructions, I place nine tablespoons of tin oxide pre-polish powder into the shaker:
Adding tin pre-polish powder to the shaker.
The shaker is half-filled with water, the lid screwed on tightly, and the mixture is given a good shake (over the sink in case of leaks). I have found this to be the best way to mix up both pre-polish and pro-polish, having one shaker for pre-polish and one for pro-polish to avoid contamination:
The result of shaking the powder and water to mix them. The powder settles quite quickly so the mix needs to be poured into the barrel very soon after it is ready.
Colin Simmons states in his Instructions sheet that the resulting mix should have “the consistency of household paint”. I pour that into the barrel until it just covers the stones and the beads are floating:
The top can then be placed on the barrel and it can be put to tumbling:
As always, I record all of this in my tumbling log:
I try to tumble a pre-polish batch for a period of between five and seven days, even though Colin Simmons states that it is okay to tumble only for three days (as the minimum). In this case, I took the barrel off the machine in just under six days (five days 19 hours to be exact). I place the pre-polish shaker in a large shallow blue plastic bucket with the sieve over it (Note, January 2022 – I have just come across a suggestion from an experienced polisher that it is better using a plastic colander or sieve, not a metal one, to rinse stones at the polish stage as the metal ones tend to put metallic streaks on the stones. I am considering making this change):
I clean the blue plastic bucket before use in case I need to pour off any spillage back into the container. When the contents of the pre-polish tumble are poured into the sieve, it can be difficult to direct the liquid into the shaker container, which is why I don’t use the plastic “safety” colander for this. A plastic sieve may be better than a metal one for this.
Opening the barrel, I pour the contents into the sieve, allowing the pre-polish mix itself to drain into the shaker. Most of the liquid will end up in the shaker but if too much gets away, into the bottom of the bucket, then the bucket may need to be tipped up to pour it into the shaker:
I note on the shaker the date when the mixture was used. The pre-polish powder eventually settles at the bottom of the shaker. The mix can be re-shaken and used again, at least five or six times:
I then place the sieve over my usual red bucket and wash the stones and beads with fresh water and put them back into the tumbler barrel for a soap tumble:
I use a small sieve (or my fingers) to recover any stray plastic beads that have escaped into the bucket, before discarding the water:
Once all the stones and beads are back in the barrel, I add water and a few gratings of sunlight soap, put the top on, and then start the barrel tumbling again. This washes both the stones and the barrel in preparation for the next stage, to avoid contamination:
I usually do a soap tumble for at least three hours, maybe as long as a day. In this case, I ran the soap tumble for just under 20 hours:
I wash the soapy water from the stones and plastic beads:
The water is a grey colour afterwards, and there are more escaped beads to recover:
I place the stones on a paper towel to dry prior to inspection and sorting in preparation for the pro-polish stage. They now retain a shine even when not wet:
I complete the tumbling log entry, adding the time for the soap tumbling. This brings Stage Five to completion. The next Post looks a little more closely at the stones at this Stage, comparing them with how they looked when collected.
