Updated: Jan 31
I recently added the option of finishing glass pieces with various grades of loose grit to my glasswork. It’s been an educational and satisfying process. And since I can’t begin to afford the coldworking machines that would allow me to do production finishing – at least not yet – working this way, other than borrowing space in a friend's sandblaster, is the only other option I really have for varying the finishes on pieces. I've chosen (below, left to right) silicon carbide in 220, 400, and 600 grit sizes, and mirror-grade Cerium Oxide. (Note the repurposed Talenti ice cream containers, which, in addition to being great for frit, were perfect for this.)
You may be wondering, Why would you need to change the finish on a glass piece? Glad you asked. There are several reasons to change what either comes out of the kiln or off the saw or grinder.
1. To remove burrs, chips, or other marks from tools or kiln processes. I have used a 400-grit diamond sanding pad to great results for just these reasons. Sometimes, jewelry and other pieces can have small needles or burrs which must be removed for safety reasons (as well as cosmetic ones). But the pad is often too large to get into tight spots, so loose grit it the next best way to get at these problem areas, often with a “scrubby” pad and a bit of water added to the grit to make a paste-like slurry.
2. When it’s no longer possible to change the appearance of the piece in the kiln. This happens when the piece has already been slumped, draped, or otherwise formed. For instance, if I needed to fire-polish one area of a slumped bowl, I'd have to heat the piece to 1,300 degrees Fahrenheit, which is past the normal slumping temp of 1,250 degrees Fahrenheit, and the bowl would change considerably from its original slumped form. So it's loose grit to the rescue. Or if I need to (or want to) cut the rim off a bowl, that rough edge left over has to be ground down, and loose grit made into a slurry on a scrap piece of glass is the ticket, all the way to a mirror finish for the edge.
3. When a matte finish or no gloss at all is appropriate to the piece. When I first started my journey with glass back in 2014, I thought that all glass pieces should be glossy when finished. But I have since learned and come to appreciate those works that don’t have a shiny, glaring finish. This matte effect can be accomplished quickly in a sandblaster, but since I don’t have one, 220, 400, or even 600-grit silicon carbide worked by hand will do the same. Each higher number, or smaller grade of grit, produces a finer and finer matte surface, but none of the color of the piece is lost. One example where I intend to use this in the future is to replicate a fragment of wall from an Anasazi dwelling, and this is exactly what it should look like.
4. When the work requires several kinds of surface finishes. I haven’t yet produced anything that meets this qualification, but it’s possible. And I’m sure someone else has. This would be difficult in a kiln, though it could possibly be done easier in a sandblaster with the proper use of resist in just the right places.
5. When a matte finish brings out highlights that glare would make hard to see. The example below is a custom piece that a friend actually wanted to stay glossy (left), but you can see the difference in how a matte finish brings out the highlights of the shards of iridescent glass and makes them easier to see (right).
I accomplished this suggested effect simply by holding the piece of glass I had been polishing on with 220-grit above the customer’s piece; it scatters the light just as a matte finish would do.
So my first foray into working with loose grit was making short drinking