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Has anyone ever tried polishing glass with a sandblaster?

I've got some pretty good polish routines down for my handheld pieces, but my big castings are way too large for the machines and the handwork is handnumbingly extensive. I'm wondering if a small sandblast cabinet could be set up to first clean up the work (as with a sodablaster), then smooth and polish the piece from 220 grit all the way up to 600/alumina prepolish? (I'm thinking it would be awfully expensive to load the blaster with that much cerium, I'm not sure if you could get the friction action that you need, and anyway I don't want a high polish).

There's gotta be a reason why this isn't being done much--I suspect it's because it's too hard to prevent cross-contamination with grits--but I was just curious to see if anyone's tried it?

Hi, I really think it has to do with the costs of the medium. I think it would be great, if one had the space, to have a couple of cabinets, one with a course grit and one with fine. I get enough dust with the 220 grit, I suspect that 400-600 would just make a big dust mess.

I get a decent finish with the 220, which breaks down a bit anyway, and then use the "Tub and Shower Gel" I wrote about a couple of years ago. I makes a very nice sheen.

I tried using walnut shells and corn cob media in the blaster but without much luck.

Maybe polish it up with some jet puffed mini marshmallows . . .

It would leave an irregular surface. Think about it this way - if you sandblast a pristine surface, you create a rougher surface. If you start with a rough or irregular surface, you make a more irregular surface. Any irregularities become magnified. Sandblasting is a bunch of individual particles beating on the surface at high speed... each particle fracturing the surface a bit differently than its neighbor. Even if you make the particles very small, each particle takes a small bit of material off the high spots, and its neighbor takes a small bit of material out of the low spots.

There's a reason why it's not used that way.

Tony

But if you could apply the blaster evenly enough...? I actually want the irregular surface (or at least a version of the surface I'm starting with, not one that's perfectly flattened).

Reason I'm asking is that I'm having great success with vibratory tumblers in taking the surface down very evenly, so that the details reduce along with everything else and are therefore mostly preserved. The problem with most polishing methods is that they DO just hit the high spots. If you cast the kind of detail I cast, polishing by hand is tedious and way too time-consuming. The vibratory tumbler gives me a high-gloss polish of the detail with no flattening, as long as I control grits and time.

Problem is, a vibratory tumbler big enough to do a 40-pound glass sculpture would be prohibitively expensive (for me), even assuming you could find a media for it that could cushion the impact of a 40-pound chunk. So I was looking around for other things that don't just take down the high spots...

It would be cool to make a slow-working liquid abrasive blaster. swirl it around or spray it with velocity or both. There are a lot of patents out there on related processes like water-jet cutting. But there doesn't seem to be an application quite like your requirement.

I really like that idea Don. A spinning slurry of water and 400 grit SiC. That would do the job.

Cynthia,
I misunderstood what you were asking. I think a siphon blaster with 400 grit SiC would work well... Just need to do an experiment to verify.

Tony

The problem is the finer the grit the less mass each particle has and the less work it can do.

Have you tried the soda yet Cynthia ?
I've tried the range of grits, to pumice and cerium. Very messy and not successful.
Soda worked a lot better than 400 or 600s/c. especially after a SiC 200 blast.
Who else has tried soda?
Peter.

I saw an artist using an equal part (with plaster and silica)
of alumina hydrate in her molds. The finish of the work after demolding was as good as any acid polished surface I've seen.

Kevin Midgley wrote:The problem is the finer the grit the less mass each particle has and the less work it can do.

Absolutely Kevin. There's very little material removal with the higher grits.

Tony

It becomes a bit of a game as to how long you sit there with the piece in the sandblaster shooting dust at it vs how much time you'd spend polishing with a felt wheel and rouge or cerium.
Better to make moulds that don't require glass finishing work on the finished piece.

http://www.ebay.com.au/itm/SAND-BLASTER ... 2ea8051ac7
I got this half the price at a cheap car tool place, and a big pack of bi carb soda at the supermarket.
Well worth the try and experiment.
I'ver now bought a pressure pot, put a holey adapter in the bottom, and a bag of soda from the sandblast supplier.Ready for when I can clean out the oil in the tank and have time to get into production.
From my inet research when the soda hits it bursts sideways, not digging in, hence the minimum damage in paint removal. And I like what it does with glass.
Peter.
ps. Its harmless, to people and the enviroment.

Peter,

I recently bought a new pressure pot and have a second cabinet, I plan to experiment with the soda blast soon. I like the possibilities you've spoken about.

I'll let you know the results.

Rick

Rick.
Some things I found.
Soda wont cut into untouched glass, the ?skin needs to be broken. That said its main benefit is smoothing or semi polish, and you dont need to mask the untouched glass.
It packs down into the pressure pot, so some pros have a rocking/shaking mechanism. I'm trying a pipe with holes that goes up into the pot, so it feed from multiple spots not just the bottom. Referred to as "Ingas adaptor" on the cutting edge sand blast site.
I look foreward to someone else having a go.
Peter.

Good to know, I'll try it with the syphon feed as well as the pressure pot.

Hey, Peter;

Nope, haven't tried the soda blaster yet; I'm thinking I need a separate setup from our SiC blaster to avoid cross-contamination. (And the blaster's at Carol's house, so the logistics of setting up a second pot with separate media are a little complicated anyway)

I think I'm probably headed that way, though, if only with a tabletop unit.

Kevin, I do have castings that come out of the mold needing no additional cold work, but they're pretty rare. Coldworking is just part of the sculptural process, and I think that's the way it is for most glass casters, so making better molds isn't really a direction here.

And yep, the finer the grit, the less work it can do...but isn't that true for just about any kind of cold work involving grit, and why you don't try to remove a half-inch of glass with a 400-grit lap? What would be different about blasting?

Anyway, thanks all, this has definitely given me food for thought.

Hi Cynthia.
My first try with the little gravity fed pot was in the back yard. The dust is harmless.
You've got summer over there, and we've seen pic's of the bad forest fires. As we learnt, when you get extreme temps and winds you can get superfires that move faster and hotter than what we were used to dealing with. Terrifying for everyone involved. We feel, and some of us pray for folks involved.
Peter.

And yep, the finer the grit, the less work it can do...but isn't that true for just about any kind of cold work involving grit, and why you don't try to remove a half-inch of glass with a 400-grit lap? What would be different about blasting?

Nothing. But look at the title of the thread. Ain't gonna happen . . .

I've gotten several private messages about the "tub and shower gel" that I used for providing a nice sheen on sandblasted pieces. It's a shame that the archives got corrupted - there was so much good info there. However, I did write an entry in my blog on this several years ago.

http://glassmusings.blogspot.com/2009/0 ... -nice.html

This stuff "Clean Shield" is used to coat the insides of tubs/showers to keep water spots and dirt from sticking. Never tried it for that, but it works wonders on sandblasted or etched surfaces. It keeps fingerprint marks off, dust from settling in the pits, and gives a nice sheen.

You can't seem to buy the stuff in stores, at least around me, and the shipping costs more than the product. I went in with friends and bought a few tubes to share shipping costs.