Dry Polish Caking on rocks - any suggestions?

[Warzy Raptor]

I’m running a batch of fluorite through dry polish and annoyingly I’ve got a situation where the polish seems to be caking onto the rocks instead of actually polishing them. I’m stumped - they were all clean and bone dry when I put them in, it’s corn cob media with RockShed AO polish, and it’s been dry for weeks here so I don’t think the general humidity is a culprit.

I’m re-washing all the stones in Borax to hopefully give them a little more surface slipperiness before I try running it again, but in the meantime - anybody ever run into this issue?

[titaniumkid]

No answers but following along because I'm interested in dry polishing.

How much rock was in your barrel prior to adding the corn cob?

[lordsorril]

I haven't seen that before, but, based on your description you may be experiencing some sort of static charge that is making the particles 'sticky'.

[roy]

anytime you have rocks rubbing together it will build some heat mix that with outside temp and you'll get condensation thats my thought anyway

[Rockoonz]

Try adding a little baking soda.
No idea if it will work, but I recently had a customer at the Buckeye show tell me baking soda solved all tumbling problems, so I'm adding about a tablespoon to my 15# barrels to see if we notice a change, but the random way we tumble I doubt I'll notice. Maybe our more attentive tumblers will try it and report back.

[titaniumkid]

I found a great tutorial video by a local RTH hero that also has some polish caking. I'm unsure if caking is a problem with dry tumbling in a vibe (no one with rotary videos has mentioned it), but perhaps check your barrel to see if polish is also caking inside it. I just started some temperamental rocks in dry in a rotary. I'll let you know if I also get caking.

[lapidary1234]

Are you using the actual "vibra-dry" abrasive compound or whatever its called (from diamond pacific)?

That is the only "dry" polish I've heard of. If you're just putting silicon carbide or alumina oxide in the barrel along with walnut shells that might be the problem.

Apologies in advance if you are using the purpose built product. I've honestly never used it so can't give you any tips other than I've heard you need to fill the barrel pretty much full with it and it's supposed to be reusable (its expensive).

[titaniumkid]

I just finished some rocks in 1500 AO pre-polish that I ran with corn cob. I didn't have any grit caking on the rocks, so it makes me wonder if this is a vibratory issue (I ran them in a rotary) or if perhaps there were too many rocks in your tumbler. I only tumbled about 1/3 of a barrel of rocks because I really did not want them crashing into each other; perhaps if the rocks are crashing together too much, they cause stickiness with the polish (for some of the reasons suggested above).

And it might also be that I wasn't using polish. I'll be trying tin oxide polish this week. I'll let you know if I get caking.

Please let us know how you're going. There isn't a lot of info available on dry tumbling rocks.

[Warzy Raptor]

Hey all, sorry I posted and disappeared; ADHD brain!

So the dry polish technique I’m using is dry corn cob media in the barrel until it’s almost full, then 2 TBSP of AO polish (Rock Shed’s) per pound of media used. My 5lb vibratory tumbler holds about 3lbs worth of corn cob media, so it’s 6 TBSP of polish - it sounds like a lot BUT you can re-use the dry polish mix a number of times.

I have two going theories after some testing; one is that the dry polish mix I had was just at the end of its useful life and there was too much powdery stuff mixed in from multiple uses, which caked on the rocks. The other theory is that exposure to the ambient humidity of my tumbler area (which is in my basement) made the media a little sticky. I admittedly had it sitting in an open container, my basement humidity is kept at 50-55% but the dehumidifier isn’t close to where my tumbler station is. Ziplock bags only from now on.

I discarded the previous polish media batch and mixed up a new one, which I set up in the vibratory last night with some Fluorite (only 12 stones; important not to let them knock together.) I’m going to check it tonight to see if there’s any caking, then let it run through Thursday - four days seems to be a sweet spot for the dry polish. I’ll come back with my results; fingers crossed bc I have two nice blue pieces in there and a gent who wants me to use one to make his daughter a necklace like Moana’s!

[lapidary1234]

I haven't ever tried doing a dry polish so take this with a grain of salt. That out of the way, I can see two or three possible scenarios happening.

First off, if trying a dry polish its probably best to use a product designed and tested for that purpose. Diamond pacific makes a product (I believe its called "vibra-dry" or something like that).

Beyond that, your hypothesis that its ambient humidity could be at play.

What I think is more likely is that the walnut shells have retained moisture and its transferring to the ao. AO is used (in rock tumblers at least) as a slurry requiring water. This likely helps it move across the surface of the stone better than a powder would. There are possibly chemical reactions that occur when exposed to water but that im unsure of.

[titaniumkid]

lapidary1234 There are various tutorials on YouTube, rockshed.com, and here in the forum on dry tumbling using corn cob (or walnut) media and a standard rock tumbling polish. Lapidary supply stores that sell corn cob media will often state that it can be used with rock polishes, but they dont seem to be pushing a dry media specific polish. I haven't come across a dry specific polish yet, but I'd be interested to know more.

The polish doesn't require water to polish the rocks. Instead, the dry media acts as a surrogate for water by distributing polish and helping it contact the rock surface while keeping the rocks better suspended than when using water as the media. In water, the rocks falls and bash against each other, which prevents more fragile rocks from getting a shine because they get bruised. The rocks minimally touch each other when tumbled in dry media (I can't hear them bashing or grinding against each other at all right now, which is perfect! And I know it is working because these temperamental rocks came out of AO pre-polish looking shinier than when they went in).

The theory about humidity could be correct. It has been tropical here lately, but the media I used was brand new and nice and dry. I can imagine it absorbing water if left out in the open.

[Warzy Raptor]

Dec 2, 2024 23:11:36 GMT -5 titaniumkid said:

lapidary1234 There are various tutorials on YouTube, rockshed.com, and here in the forum on dry tumbling using corn cob (or walnut) media and a standard rock tumbling polish. Lapidary supply stores that sell corn cob media will often state that it can be used with rock polishes, but they dont seem to be pushing a dry media specific polish. I haven't come across a dry specific polish yet, but I'd be interested to know more.

The polish doesn't require water to polish the rocks. Instead, the dry media acts as a surrogate for water by distributing polish and helping it contact the rock surface while keeping the rocks better suspended than when using water as the media. In water, the rocks falls and bash against each other, which prevents more fragile rocks from getting a shine because they get bruised. The rocks minimally touch each other when tumbled in dry media (I can't hear them bashing or grinding against each other at all right now, which is perfect! And I know it is working because these temperamental rocks came out of AO pre-polish looking shinier than when they went in).

The theory about humidity could be correct. It has been tropical here lately, but the media I used was brand new and nice and dry. I can imagine it absorbing water if left out in the open.

Yup, titaniumkid nailed it! I’m also interested in this vibra-dry though, I have to look into it 👀

In good news, I checked the Fluorite in the new dry media polish this morning and not only was there no caking on the rocks (although there was some on the tumbler walls), but the rocks had already taken on a fantastic shine! So either my previous batch of media had worn itself out, or it had just absorbed the ambient humidity - or a combination of both.

Great lessons have been learned here today! Once I finish running all of the Fluorite through I’ll get some photos and drop them in here. (Somebody remind me to make a video on dry polishing too.)