Can you polish with Silicon Carbide: YES

[chaosdsm]

Fact is, you can polish just about any material (even dirt - seriously search youtube for dorodango) with just about any abrasive, if you use the right technique.

So, how about tumbling with SiC, can it polish rocks:   DEPENDS....

EDIT 9/28/2024: So, this result was achieved through wet sanding with diamond sharpening stones up to 1500 grit, then switching to wet sanding with silicon carbide sandpaper with: 3,000, 5,000, 7,000, and 10,000 grit papers.  No "polishing" or burnishing of the stone just straight water and sandpaper, rinse off & let dry.






NOTE: I flipped the image in photoshop to see that I could easily read the quarter from the reflection off the sanded stone.

I've been running a dry vibratory tumble for about the last week & a half

Stage 3 with 500 grit SiC in the Eastwood 18lb vibe with included bowl.  I think the results would be better with a 500/600 blend or even a 600/800 blend.  With rocks smooth but very much a "flat" sheen to them, I put them in the new Eastwood 18lb tumbler checking on them daily, at the end of 1 week, most of the rocks had developed at least a matte sheen, some an eggshell sheen, and a couple even a satin sheen - think paint...  From dullest to shiniest: flat > matte > eggshell > satin > semi-gloss > gloss > high-gloss

Stage 1 pre-polish with 1,500 grit SiC, in the Eastwood but with the UV-18 industrial bowl.  I was out of town all day yesterday, so didn't do first progress check till today, about 36 hours after start, and was I surprised at the results so far.  



Weight is about the same for both stages run: there's a mix of Labradorite, Petosky, 8 or 9 pre-polished agates - very well rounded & ultra-glossy (so they should act mostly like filler to the other rocks), but felt like they had a plastic-like coating on them which I didn't like.    In the Stage 3 I had about 2lbs of those large oblong ceramics, I swapped those out for about 2 pounds of 10mm round ceramic sphere's in my pre-polish stage 1.  I then filled in the rest with corncob & about 2oz of SiC grit.  

If only I could get my hands on some 15,000 grit SiC I would try that for the final polish stage.  EDIT: OH....  found and purchased some 1 micron SiC.....  

[pebblesky]

Great experiment. The stones you tumbled are challenging. I would love to see the results of Labradorite and Petosky.

When I did a vibe run with 120/220 SiC as stage 2 for a week, I got some reasonable shines on my common agates and jaspers. Especially for the hard rocks with pebble/sphere shapes, they could be described as glossy but not highly glossy.

vegasjames described tumbling the Candy Rhyolites with water only and after a month, they became shiny.

[vegasjames]

Here is the water tumbled candy rhyolite.

[chaosdsm]

Sept 10, 2024 0:03:42 GMT -5 vegasjames said:

Here is the water tumbled candy rhyolite.

That's incredible!!!

[chaosdsm]

Here's some of the other rocks I pulled out that I didn't get a chance to edit/post last night:



To my eyes, the sheen on these is as follows: 

the Labradorites are satin to semi-gloss,

the two larger Petosky's are satin, the smaller one is eggshell 

the black speckled stone is semi-gloss 

Again, this is after tumbling in 1500 grit SiC

[chaosdsm]

500 grams of 1 micron green silicon carbide ordered!

[chaosdsm]

So, this result was achieved through wet sanding with diamond sharpening stones up to 1500 grit, then switching to wet sanding with silicon carbide sandpaper with: 3,000, 5,000, 7,000, and 10,000 grit papers.  No polishing or burnishing of the stone.




NOTE: I flipped the image in photoshop to see that I could easily read the quarter from the reflection off the sanded stone.

[chaosdsm]

I got the 1 micron SiC powder in today!   I split my rocks into two groups.  The first group I put in with 12,000 grit AO polish which ran for 75 hours @ 7.05kWh.  
 
So I'll run the 1 micron SiC powder group for about the same, then I'll post comparison shots.   I saved 1 piece of Labradorite, and 1 piece of Petosky from going into either batch, these two rocks stopped at the 1,500 SiC powder.  




Purchase was for 500 grams (about 1lb 2oz) of 1 micron silicon carbide powder.  The mylar bag, paper label, & inner cellophane bag probably weight between 8 & 10 grams, so this looks about right!  Fairly expensive at $81.67 per pound, about double the price of 0.8 micron Cerium Oxide, but a bit cheaper than the 0.3 micron micro-alumina A polish @ 109 per pound.

[chaosdsm]

So... this is kind of a set-back.... but also not really....

Meaning, this didn't turn out to be the apples to apples comparison that I hoped it would be, instead it's more of an apples to oranges comparison  

My polishing media for both was supposed to be the fine grained corncob media that came with my Eastwood tumbler + 2oz of 12,000 grit AO in the first bowl, and 2oz of 1 micron SiC in the second.   I put what I though was about half the bag of corncob in with the 12,000 grit AO polish, but that actually ended up being closer to 75%.  So the 1 micron SiC didn't have nearly enough corncob in the bowl for good movement, so I ended up putting 2x the ceramic balls in the bowl to get the movement right.     I should have started by weighing everything out to get things as close to equal as possible   



The three Petosky's on the right are from the 12,000 AO, the two on the left are from the 1 micron SiC, the other two were stopped at 500 SiC. Although the AO & SiC look nearly the same here, in person the AO stones are definitely shinier.


This photo gives a better representation of what I'm seeing, the right stone run through 12,000 AO, the left the 1 micron SiC.  Honestly, the 1,500 SiC result was better than the 1 micron SiC result....

So I gave up, and switched to a wet process, & I'm doing the entire process over, started with 220 grit yesterday morning & will run it till Saturday, I'll then switch to 500 SiC, then 1,500 SiC, before splitting the load in half & finishing half with 12,000 AO & other half with 1 micron SiC - doing 3 days for all stages.  

This time I'll remember to weigh out the rocks and filler to get both halves as close to exact as possible for the final polish!

Also found a method of keeping the rocks wet without continually adding water!  I have some 3/4" thick closed cell EVA foam that I cut to fit inside the Eastwood lid, which fits just right over the Lyman plastic bowl.   Being plastic, it's impervious to water.... and being closed cell foam, the EVA does not absorb water, and with the addition of some soft rubber spacers sealing up the bowl completely, it keeps all the moisture trapped inside the bowl!!! 

 I spent about an hour Wed morning making sure I had the right amount of water in the mix.  I checked progress at lunch today, & it did not need water, I checked again after work, and all is still good, that's about 36 hours without adding water!!!

[chaosdsm]

Here's a short clip I made of the 220 grit running.  Anyone experience foam in their vibe tumbler like this?  

[Peruano]

I suspect too much water in contact with a healthy amount of soap. Not necessarily a bad mixture. IMHO

[chaosdsm]

Sept 27, 2024 6:35:19 GMT -5 Peruano said:

I suspect too much water in contact with a healthy amount of soap. Not necessarily a bad mixture. IMHO

Possibly right on the too much water, though the mix never really showed any negative signs that I saw, but that might be because of how powerful the motor is. 

No added soap in this run, but there could have been some soap residue that didn't get completely rinsed off my ceramic filler.   I've used Dawn Ultra at 1/2 Tbsp per pound in a couple of my rotary tumbles.  Makes for a nice thick foam that seems to keep the grit suspended, and seems to make it last a lot longer, i.e. no soap in stage 1 = no noticeable grit remaining after 7 days, with soap in stage 1 = quite a bit of noticeable grit suspended in the foam, and at least the same amount of progress.  However, I'm thinking that in a vibe tumbler, it may cause to much grit to be suspended above the tumbling action...

Just checked on the current progress, nearly 60 hours runtime, and still no need to add water!  There's a pretty thick layer of slurry building up on the sides & middle of the bowl, though the rocks are still moving around quite well, and the slurry seems a little thicker and stickier than it did last night.