Abrasives  

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It's called "carving" because you're cutting...
not beating the glass into submission!

Sand Blasting??

Here’s the "cutting edge" in glass carving! Just because this process is called "sand blasting" don’t think for a minute that what is used is really sand - however when I clean up parts on the travel trailer I do use sand, but that is really out of the picture for glass. Sand is not sharp. It's great for "beating" rust or paint of objects, but when it comes to class, the idea is to "cut" it, not beat it into submission! Can you use sand for glass? Sure, but don't expect clean edges, because the beating effect is actually chipping instead of cutting away from the blast area.

Grit - the size of the abrasive.

Abrasives come in many sizes (grits) and colors. The color really has little to do with it other than helping me identify what I’m using and keeping it separate from the others.
The grit size has much to do with the "finish" that is left on the glass after blasting. It might be a rough finish with a large grain pattern or it could be soft and smooth as silk with a grain pattern as fine as milk.

Grit is rated from the smaller numbers being the most course to the larger numbers being the finest. The normal range for use in glass carving is from about 80 grit to 150. The use of different grits and different types of abrasives can yield many and various shades, patterns or tones to a project.

Various Abrasives...

Crushed Garnet

Probably the most common (and cheapest) abrasive for blasting is crushed garnet. It has a beautiful light ruby or dusty rose color. I have used it for years and by controlling the grit size you can produce wonderful pieces of art with a multitude of shadings and textures.

Silicone Carbide

Another abrasive that I had in my garage for years and didn’t even know it, was silicone carbide. I had been using it to polish rocks. By gradually increasing the grit size, it would polish the rocks over the period of about a month. Silicone carbide is black for the smaller grits, or a gun metal color for the larger/finer grits. I noticed when I used it to blast with that I could actually see a glow where the abrasive hit my glass! Cool! It was sort of like having a headlight on your blasting gun!
The draw back was that it was SO abrasive that it ate right through the masks I used in a very short period of time. I was intending on using it mostly for cutting into stone, so I was using about an 80 grit. I’m sure the finer grits would have been less detrimental on the masking. This just meant I needed to upgrade or double my masking.

Aluminum Oxide

What I find myself using mostly now is aluminum oxide. It has a great cutting ability, leaves the glass smooth as silk when using 130 - 150 grit and retains it’s sharpness. It's not really much different from the silicone carbide in my opinion -- either of them work great. The benefit is that they are very reusable and the grit retains it's sharpness as it breaks down. Over time your 80 grit becomes 100 and then 120 and so on. Not a problem and takes quite a bit of use.

Sand

You can get bags of "playground sand" for only a couple of dollars. It is great for getting the rust of lawn furniture, trailer hitches, old tools and the paint from almost anything. However sand works on the "beating" principle rather then the "cutting" principle
.
For some projects, like dulling the surface on ceramics, you can get white sand. It's finer and softer than the playground sand.

The Cutting Edge...

Sharpness is the factor of the abrasive that does the cutting for you. All the abrasives mentioned above have excellent sharpness. I recycle all my abrasives and reuse them many, many times. Some of the crushed garnet I have been using for 8 years! The crushed garnet, however, does break down in time and you find yourself with a much finer grit than that with which you started. But it does remain sharp as it breaks down.
The aluminum oxide and silicone carbide I have not found to break down (or at least very little) and it has retained it’s sharpness very well over repeated uses on glass and stone.

Sand, on the other hand, has little sharpness to begin with and breaks down almost immediately. It’s great for getting the rust of the lawn furniture before you repaint or for special, very rough, textures on glass - but I don’t recommend it at all.

Price???

Price wise, crushed garnet is the most affordable at about $20 for a 50 pound bag. The aluminum oxide and silicone carbide can run $1.25 to $1.80 a pound. To keep your blaster running for more than a 10 minute interval before refilling your abrasive you need at least 20 pounds of abrasive in your siphon blaster or 40 pounds in your pressure pot. Sand is dirt cheap - no pun intended - about $2.50 for a 50 pound bag.

Check the Suppliers section in the menu for locations to order abrasives.

Keeping Abrasive Clean

Cleaning your abrasive before reusing it is very important. Find yourself a nice piece of filtering material - a doubled over piece of screen door screen works fine for me. Cut both ends out of a 1 pound coffee can and tape the screen to the outside bottom. Use this to filter your abrasive before returning it to the blaster for another use.

Generally, the parts of the glass or stone that you are blasting off are pretty fine. However, when I do brick or concrete, I find the chunks get a little large and my filtering process is critical. I have seen the damage when a chunk of material goes flying through the blaster and hits the center of a 30" x 40" nearly completed piece of glass! For you guys out there - yes, there is an appropriate time to cry over your work!

Dampness

One last comment, if your abrasive becomes damp you will have problems with flow control (the amount of abrasive - if any - that comes out of your gun). Abrasives can pick up moisture from the air so keep it in dry, room temperature areas or air tight containers. It can also pick up moisture from the air in your compressor. You need (as mentioned in the equipment section) a water trap on your line to remove excess water that accumulates either in your lines or directly in your compressor. (sometimes more than one trap if you have long lines from the compressor.

You can dry abrasives by putting them in shallow baking pan in the oven at low temps for an hour. This cooks the moisture right out - but the stuff gets real hot so watch it when you handle it!