Ultimate rotary polish comparison test?

Since this test began, in normal tumbling I have finished perhaps 50lbs of polished rocks which are in containers in my house in addition to all others I've done. This test has been so revealing, that I'm leaning toward expanding it into other polishes. As one example, what might happen with using only ground walnut shells? I have the methodology developed, and have kept all the rocks separated, so my mind is already on the next saga which I might start this fall.

Associated with that is what have I learned about the materials and which ones matter for comparisons and which don't? I looking at all the shiny rocks laying around in my house, one thing comes to mind. All the quartzes, more or less, are in one group and there is probably no need to split up that group. It seems they are all tight and smooth after grinding like I do to perfection, and either they polish, or they don't so well. But the whole batch is almost always alike, and, they almost always polish superbly. Also, even if there is some rock that breaks they still almost always polish superbly, rather than being damaged by that broken rock.  Maybe it's because they are all so tough.

They all have the perfect shine, or maybe not, but there just isn't variation within the batch it seems. This includes various categories we mention--the agates, jaspers, cherts, onyxes, and misc. uncategorized chalcedonies (like fire "agate", Moss "agate", Binghamite, Damsonite, etc. It also includes petrified organic material such as pet wood, pet coral, Larsonite, etc. This is the same as saying I see no reason in general tumbling to tumble or polish them separately from each other and indeed that has been my practice for years and with good results.

From my small experience, all these materials are some of the easiest to process and get a great shine, even with no cushioning used at any stage, including polishing, if there is sufficient size variety including plenty of smalls. I see no reason really to have to use more then one of them in the test going forward.

However, there is one subgroup of quartz that behaves uniquely and, to me, doesn't share all the above. The macrocrystalline quartzes such as amethyst, smokey quartz, rose quartz, etc.--at least the material I seem to get or find--is touchy. The surface almost always has tiny crevices remain here (edges of fine fractures mostly) and there even after careful grind up to prepolish. And it's brittle and can chip. And sometimes a polish run with it goes well, and sometimes not. When it goes well, it's equally shiny or not as shiny as all the other quartzes. I tend to think any challenge in polishing it perfectly is more of a cushioning issue.

So my thought going forward on this category is to have only: 1 agate or 1 jasper, and maybe 1 macrocrystalline quartz such as mentioned above. Ironically, I had smokey quartz ready for this test, 4 nearly identical piecea about the size of a grape, and somehow forgot to include it.

The fewer different rocks in my test, the larger specimens I can use too which might be beneficial.

If anyone has guidance or criticism on this idea, please mention.

I had meant to include for that large quartz group what polish the literature had recommended the most. It was alum, but with some exceptions.

It was cerium for Pure Quartz (Rock Crystal), the onyxes, Fire "Agate", petrified wood, and "Turritella agate".

It was tin for pet corals.

I could find nothing in the literature for Binghamite, Chrome Chalcedony, petrified algae, pet feces (Coprolite), and pet fossilized fern. For petrified dinosaur bone, although I found no polish recommended I did find mention that specialized methods were typically needed but those were not explained or I didn't make a note of them.

Another group is Glass which can be divided into Man-made glass and naturally occurring glass called Obsidian. Because so many tumblers experienced with Obsidian have mentioned how touchy Obsidian is, I'm not inclined to do any more polish testing that doesn't include both of these kinds of glass. They have also mentioned that Obsidian polish results have varied with the type of Obsidian and even between batches and different pieces of the same type. So that's why I chose Apache Tears Obsidian that had come from the same purchased batch. If that isn't done, I guess the ideal would be to cut up an individual piece into separate pieces to test to make sure all the same.

I hate to see it end!

Bob,

I've followed the thread from the start. So very impressive! One question I had, and maybe I just missed it - when you use a polish other than Aluminum Oxide what do you use for your pre-polish. For example, if I was going to use Tin Oxide is it still ok to use Aluminum Oxide as the pre-polish?  Is there a Tin Oxide pre-polish? Maybe a pre-polish makes no difference provided we're talking about a  1000-1200 any pre-polish grit. On the other hand, I wouldn't use 500 grit Silicon Carbide ( sharp edges I think ? ) over 500 grit Al Ox...

Thanks

For all who have followed this, I wanted to share what I'm thinking about doing next. All the test rocks were kept as is. I'm thinking about doing a burnish test so see just how well it works on all these materials. To do this, I would first take them all back to unpolished by a run in 1,000 grit. Then I need to polish them all to get them ready. I guess the way to do that would be to polish them in the polish that did the best for each.

Then take the polished rocks and divide into 2 groups, which would allow for 2 rocks of each type. One group would be the control group to just remain. The other group would be to be burnished and then photograph the comparison results.

Another option would of the 4 rocks of each type divide them as follows:

Group 1 control group do nothing after polished again.
Group 2 burnish for what I typically burnish for 12 hours (or 24 hours?).
Group 3 burnish for something less than that, such as 3 hours.
Group 4 burnish for 3 days or something like that.

If anyone has better ideas, I'm listening.

You will find a wide variety of approaches, but what I do is probably typical or average.  After polish, rinse, then burnish with Ivory soap flakes carved off with a knife.  I use a full small size bar in a 12lb barrel.  It usually improves the shine a little, and sometimes quite a bit, and rarely not at all.  Some people do for only "overnight" meaning I suppose 10-12 hours.  Some for 1-3 days.  It's rare that people do more.  I have not experimented a whole lot with it myself, but so far have not noticed much difference between that happens overnight vs. going for a few days.  So I've typically done 1/2 to 1 day.  All that was about average Mohs 7 rocks.  For specialty stuff like obsidian, it gets almost mystical as to what people might do...

Hey Bob, thanks for taking the time and having the impetus to do this experiment! I have read the whole thing and love all the pics! You really can see a difference across the board and this furthers my opinion Tin Oxide provides the best polish, generally. I will now also save my polish (after rinsing and drying) to reuse as a polish or polish stage 2, since I read in here it breaks down to even finer material. That will save a literal ton of money!
Did you ever conclude the burnish experiment? What were the findings?