Silicon Carbide & Aluminum Oxide
Sandblast etching on glass is accomplished by changing the surface of the glass creating rough areas in contrast with smooth clear areas. The media, which is referred to as abrasive in our industry, will chip very small particles of glass out of the surface resulting in what is called an etch. The most commonly used abrasives are silica sand, aluminum oxide, and silicon carbide. The initially more expensive oxide and carbide abrasives are much more economical to use because they can be recycled many times and also save labor dollars due to the fact that they cut so much faster. If you are blasting outdoors and are unable to recycle, silica sand will be a better choice. Please wear a respirator when using silica.
The size of abrasive is specified in a grit number. The smaller the particle, the higher the number will be. A larger grit size (100 grit) will cut faster and will yield a more course look. Conversely, a smaller grit size (180 grit) will cut slower and give a smoother finish. The most common grit sizes for blasting on shower doors, mirrors, or architectural glass is between 100 and 180 grit.
Silica Sand is one of the most economical abrasives, but is very slow cutting and can only be recycled one or two times. Sand is typically sold in grit sizes of course, medium and fine. Even the fine grit sand contains particles ranging between 70 and 140 grit. The larger particles in this grit size can penetrate the thinner resist materials and ruin an etch job. A serious drawback to using silica sand is that it contains free silica that is considered a hazardous material because it causes silicosis, a form of lung cancer.
Aluminum Oxide is the most widely used abrasive. It does not contain any free silica and is therefore safer to use than sand. The grit size is consistent; it cuts much faster and can be recycles many times. The only drawback to using Aluminum Oxide is while blasting the oxide generates static electricity which causes dust to stick to the back of the glass you are looking through, making it very hard to see what you are doing, especially when using back lighting. A perk is the light produced by the electricity at the point you are blasting making it easier to see where the abrasive is blasting. The person blasting may experience mild electrical shocks because of the electricity that is generated especially if the blast cabinet is metal.
Silicon Carbide is commonly referred to at the Cadillac of abrasives. It is the fastest cutting and the longest lasting abrasive without any of the drawbacks of aluminum oxide or silica sand. Unlike sand and aluminum oxide, silicon carbide doesn’t dull while blasting, instead the carbide particles chip, exposing sharp new edges.