Tin oxide problem??

[kevinglenn]

First post, so be gentle! I've been a rock tumbling hobbyist for about a year now with increasingly better results. I have a 3# Lortone rotary tumbler. I am mainly tumbling local jaspers and agates found here in Georgia.
Up until recently, I have been using aluminium oxide as polish with good, albeit slow results. Lurking about the board here, I saw some good things about tin ox, so I forked over the cash and bought some.

Oh yes, tin ox polishes a lot faster from what I see, but now I have a problem I have not encountered before, and even searching this forum has not revealed a similar situation. Some of my stones now have a shiny "tin plating" for lack of a better description. It looks almost as if certain parts of the stone have been galvanized!!!

I thoroughly clean my barrel and all the sealing pieces after each step. I am using clean distilled water. I have used no additives and yet since I have used the tin ox, same thing. Nothing in my processes have changed except that I changed to tin ox. I did try adding borax to the polishing load once, but that didnt change the results. Now it doesnt affect alll the stones but it is still randomly putting patches of tin on my rocks!!

Any ideas???

[Sabre52]

Wow Kevin, that's a new one on me and I occasionally use tin oxide as a final polish. Never seen that happen and am unsure what would cause it. ( Of course now AO is my favorite as it's so good and so cheap). Are you sure the stones in question don't contain metallic minerals like hematite? The jasper I collect around our ranch has lots of hematite that polishes out to a silver or tinny looking metallic finish. Marcasite ( pyrite) also does that as do certain other metallics often found in stones. Other than that, I'm clueless as to what would cause your problem...mel

[spacegold]

It sounds to me like something is reducing some of the tin in your mix to metallic tin, but I haven't a clue what it might be.

[krazydiamond]

have you tried a burnishing stage with borax?

KD

[kevinglenn]

Thanks so much for the replies! When I started experimenting with it, I put a tablespoon of borax into the mix and suspected a chemical(been a long time since Chemistry 101 !) reaction as a result of the borax. The next two times no borax was introduced and the results were the same. I've also suspected the stones themselves because in one instance I was tumbling some brazillian agates along with my native stone and the agates were beautiful, but about 20% of the native jasper still had the blotches on them. The stuff looks like lichen on a smooth stone, only shiny like fresh galvanized tin. Thats really the only way to explain it. They do not show up until the final step either, so that pretty much hones it down to the tin ox stage.

My property where I am collecting my native rock is an area of dolomitic karst, and basically the stumps ridge/valley mountains. Its solid, multi colored and wavey and occasionally vuggy, but not translucent for the most part. (occasionally I do find agate-like stones). Anyway, iron is prevalent in the area and there have in the past been iron mines nearby. It wouldnt be a surprise if there was planty of iron in the stones I am collecting. But iron and tin have to be coaxed together, from what I understand, with electricity.
I'll take some pictures in a bit and try to post them so you can see the problem I am having - should have done that in the first place!

Thanks again for your responses!!
Kevin

[donsimpson]

You might give cerium oxide a try. Some people swear by it.

D

[kevinglenn]

Hey I'll try anything once!

Here are some pics:

the bad:


Weird huh?

Now the good, just to make me feel better ;D (with al ox):


Its baffling me as to why this is happening!! I've run this past some geologists too and they dont know either. Well, I am going to try the cerium and if that doesnt work, I am going back to the aluminum ox. Thanks for your help folks!
Kevin

[puppie96]

Kevin, are you a neighbor? This sounds like S.E. MO. I do think that I've seen this once or twice. I've also had shiny stripes/scribbles on the stone, like a pencil scribbles -- shiny gray. I do polish with tin oxide in my vibe, where polish quantities are easy, and I'd never made a connection between this phenom and the tin oxide as opposed to other polishes. It has happened rarely enough (the spot-like effect) that I wrote it off to some strange metallic inclusion in my rock, or something.

[donsimpson]

That is weird. You should try running those rocks for several days in borax and/or ivory snow to see if it will wash off.

D

[spacegold]

Please let us know if it shows up with cerium oxide. My wild guess is that there is some trace mineral in the the stone that is reducing the tin which then mechanically plates to the stone. Obviously it was not doing that with the alumina, so any chemistry likely belongs to the tin.

[kevinglenn]

Hey folks, thanks again for the responses. No these rocks aren't from Mo... they are just some agaty jaspers from NE Georgia. I've never seen stones like this before anywhere else, although I think someone told me once that there is a similar jasper in Mo. I've only seen them in the Bartow County Georgia though.

I guess I am going to go back to the aluminum oxide for the time being. I polished some blue brazillian agates that came out great with it, in the same batch as the local stone that came out bad, so there must be some sort of trace element causing the problem. I'll keep the tin-ox on hand for the agates I guess. its a shame though.. the tin ox worked wonders and did it really fast too.

Take care, and thanks for the help,
Kevin

[stefan]

Hmm At first I was going to say that it was from a wire collinder or strainer (the metal leaves a shiney patch on the rocks- that is why I switched to all plastic for strainers and buckets) but then I say those pictures!!! Yikes-
So here is what I came across so far
www.jtbaker.com/msds/englishhtml/s6410.htm
the thing is I don't think there is enough Tin in Tin Oxide to actually Plate the rocks- I think the plating is coming from something else (possibly a metal lid liner- or something that fell into the tumble?

[spacegold]

Tin oxide is primarily tin.

[rallyrocks]

spacegold said:

Tin oxide is primarily tin.

yes indeed, about 79% by weight....so as much as is shown there being reduced from a couple of tbsps of oxide is not far fetched at all.

I am curious, did the barrel swell or show any signs of offgassing or foaming in the polish? reducing the tinox should release quite a bit of 02 I'd think, unless that gets bound up in the borax solution that stays behind....

[spacegold]

Since the condition did not appear with the alumina, it is very likely a tin recuction, and whatever is reducing the tin is probably picking up the dissociated oxygen.

[stefan]

Yes but you people are talking about a chemical reaction that SHOULD not be possible in a tumbler-

[spacegold]

And why is that, Mel? A tumbler with a warm, agitated aqueous solution seems like a fruitful little reactor vessel. The water will likely not be perfectly neutral pH, so there will be a bit of acid or base ion to facilitate matters. Chemical reactions that produce gaseous by-products are common in tumblers. Why would a reduction reaction be far-fetched if the proper materials were present?

[spacegold]

Oops, Stephan, Mel, I'm sorry. I got my experts mixed up here. Can I blame it on a senior moment?

[LCARS]

Hmmm, that's an interesting situation...

It almost sounds like something in the barrel is stealing the oxygen from the TO, as far fetched as that seems...

If you want to try another "test", you could put 1-2fl oz of 3% H2O2 (hydrogen peroxide) in the polish stage when using the TO. That should satisfy any oxygen affinities in the material you are tumbling, in the unlikely case that something in the load is "stealing" oxygen ions from the polish. I know there are reactions out there that will favor oxygen bonding to one substance by ripping it off from a weaker oxide bond but that usually requires a catalyst or input of energy to make happen.

Of course, there is always the chance that the oxidizing agent used to make the TO polish you got did not fully react the metal, leaving some intrinsic tin that is coating your rocks. That is just a matter of product quality. Hydrogen peroxide is a relatively good and safe oxidizer so maybe that would help...? I have used TO before with no problems like that...

[kevinglenn]

hey I will try anything at this point. I am as baffled as you all are about it. I havent hit a polishing stage since I last posted, so I havent been able to try anything new yet.
This occurance only seems to happen on the native jaspers I am polishing and nothing else. That is another thing I find strange.
I dont use deionized or purified water, but I can't see how in this small tumbler, that would make much of a difference. In my experiments in college chemistry reducing agents needed to be pretty well saturated to cause this sort of thing to occur so quickly as to seem like electroplating.
Nothing metal is in the tumbler by the way. It's a Lortone, and the barrel is rubber, and nothing comes in contact with the material inside. As well, there was no gas buildup or anything unusual like that either. I thoroughly clean everything inbetween steps as well. Who knows!!!
The next batch I am going to polish in Al Ox - I dont expect the same results of course.