Need help with bruised rocks in vibratory polish stage?

[Warzy Raptor]

Hey y’all, so I’m a vibratory newbie and I’m running into an issue where everything is great up to the polish stage - and then in polish some of the rocks are bruising 😭 I’m running a Raytech 5lb (technically the actual tumbler mechanism is Harbor Freight’s knock-off but the bowl is the actual Raytech model), 24 hours in 1 TBSP 220 grit silicon carbide, 4-days in 1.5 TSP 500 grit aluminum oxide pre-polish, and then 36 hours in 1.5 TSP aluminum oxide polish. I’m only working with hard rocks right now (6.5-7+ on the Mohs scale), a mix of microcrystalline silicates - beach quartz and beach chert/jasper - and occasionally some amethyst or tiger eye, all rotary tumbled in 60/90 grit until they’re good and smooth. I get a good slurry going in the vibe, not too runny and not too dry, and then I spritz water in 1-2 times a day as needed to keep things moving steadily. Each stage gets a 1/2 hour burnish with the barrel half full of water and 3 TBSP of Borax, and then the rocks go into the ultrasonic cleaner for 10 minutes tops while I give the barrel a good clean/scrub.

I noticed the polish stage is always runnier/thinner than the rest, which may be contributing to the issue. I also *THINK* I may have been putting in too many rocks versus the media, previously I was doing 1 part rocks to 2 parts mixed ceramic media. I have a batch running in pre-polish right now that’s 1 part rocks to 3-4 parts ceramic media; my ceramics are mixed in size, about equal parts small/medium/large (as are my rocks.) I fill the barrel to about 1/2 inch from the top with rocks and media before running.

Experienced tumblers, help a Raptor out please! I am LOVING the vibratory but I don’t want to abuse my poor little beach quartz.

I’ve heard of people adding either Borax or sugar to their mix in order to thicken it - if I do need to try to thicken my polish slurry up, which do you recommend? Or should I try more polish? OR do I need to switch my ceramic sizes/ratios?

Sorry for the long-windedness, thanks in advance for any help you folks can offer!

[titaniumkid]

Not sure if this will help a raptor much, as I think you're already on the right track.

I don't use a vibratory tumbler and I wouldn't call myself experienced, but I would say you are right about the thinness of the polish stage slurry being an important factor. I recently achieved the same thing in a rotary. I could hear the difference between grit and polish as the rocks tumbled around, and typical apathetic Aussie that I am, was all, "Psssh, they'll be right" Spoiler: they weren't alright. Well, some weren't. Some didn't care.

Anything you can do to make sure the rocks are moving but not crashing around will be helpful.

[pebblesky]

I don't have too many happy stories about the beach rocks I hounded, but here are my thoughts:

1. Maybe share some pictures. If it is always some specific types of rocks that are bruising, maybe the rocks have mixed hardness, or are porous, or are very brittle (many quartz are).
2. The small chips that fall off during the later stages could also contribute to the bruises, while the sharp edges of these chips will not be quickly smoothened by pre-polish or polish, they can scratch the other rocks gradually.
3. "1 part rocks to 3-4 parts ceramic media" sounds excessive. Does it mean you are mostly tumbling the fillers rather than the beach rocks? What are the sizes of the beach rocks you are tumbling?

The amount of 220 grit sc, 500 grit ao and ao polish you use sounds good to me.

[victor1941]

I run a UV-18 vibe and do use a lot of media to the material to be polished with success. Several things you might consider is separating the chert and other material and polish each separately with extra media. I always want the rock/media sliding in a thicker slurry state with no banging by carefully controlling the water and therefore tumbling action. Too little and too much water will also cause problems or slow the polishing step.

[Warzy Raptor]

Jul 1, 2024 18:32:14 GMT -5 pebblesky said:

I don't have too many happy stories about the beach rocks I hounded, but here are my thoughts:

1. Maybe share some pictures. If it is always some specific types of rocks that are bruising, maybe the rocks have mixed hardness, or are porous, or are very brittle (many quartz are).
2. The small chips that fall off during the later stages could also contribute to the bruises, while the sharp edges of these chips will not be quickly smoothened by pre-polish or polish, they can scratch the other rocks gradually.
3. "1 part rocks to 3-4 parts ceramic media" sounds excessive. Does it mean you are mostly tumbling the fillers rather than the beach rocks? What are the sizes of the beach rocks you are tumbling?

The amount of 220 grit sc, 500 grit ao and ao polish you use sounds good to me.

Pebbbbbbbbssss hay again! When it comes to beach rocks, what I’ve learned is that you need to lower your expectations. Drastically. And also either ONLY pick up the rocks that don’t have visible faults or fracture lines, OR be handy with a rock saw or angle grinder to either cut or grind those pieces away before tumbling. And even then….. there are zero guarantees. BUT because of the lowered expectations, when you do get something perfect it’s a “HECK YEAH!!!” moment (I started making some rock YouTube vids and I’m probably gonna make a long-form beach rock video in the future to pass on some of the important stuff I’ve figured out as far as what to look for for different applications. For tumbling - the more smooth and round, the better.)

So 1) I actually just got this small batch out of polish and blessedly - so far no bruising! I’ll post some pictures once I finish cleaning them up, as well as photos of past problem rocks.

2) I’ve gotten REALLY LUCKY and haven’t had any instances of chips breaking off in Stage 3 and 4 (that I’ve found or been aware of anyway!), but I’m always real careful in between stages to look for that!

3) Yeah, this batch was 1 part rocks and 3 parts media which definitely WAS excessive. But hey, lots of nice shiny ceramics now, haha! My next batch will be back to normal as I test the below theory:

I BELIEVE I MAY HAVE SOLVED MY ISSUE - if I’m correct, it was in fact the polish stage just moving the rocks around too dang quickly. With this batch I tossed 3 TBSP of Borax in with the polish and my goodness, that slurry was THICCCC come the next morning. Kept a close eye on it and kept my water spritzing to a bare minimum, let the rocks move slowly but not TOO slowly (boy howdy the learning curve on the vibe is strong!), and after 36 hours gave them a good burnish. Currently running them through the ultrasonic and then cleaning any cracks/fissures out doubly with a WaterPik (because I’m a masochist who loves all things feldspar, and feldspar is always gonna feldspar), and so far ZERO bruising!

I’ll be back with some photos in the next post!

[Warzy Raptor]

Ok, I was way too lazy to do lighting and cropping and uploading and etc for photos, so I just made a video and popped it on YouTube instead!  These are just the beach rocks (I had some other stones in with them), but GOSH they took one heck of a polish and there was zero bruising!  The one rock I talk about that looks bruised has a huge inclusion pocket that JUST came to the surface and messed her up, but them’s the breaks with that type of rock - I don’t go for perfection with beach rocks bc I’ll just make myself INSANE, lol.  Anyway, roll that beautiful bean footage!

[pebblesky]

Nice tumbles! The one at 5:51 is a winner.

[titaniumkid]

I like the colours of the "chert... jasper..."

But my favourite... it's a toss-up between the commentary and your obvious delight in your rocks