Polishing Scratches Out of Glass
We are "rock people" and not "glass people". Therefore, we do not know anything about glass other than what is on this page.
Please don't call us up or email us with any questions about glass polishing, because all the information we have is on this page.
Cerium oxide is the polish of choice for glass. Before you can polish scratches out of glass, you must first determine how deep the scratches are. If you can feel a scratch as you run your fingernail across it, the scratch is too deep to be polished out with cerium oxide. You must first grind the scratch out.
The grit used to grind out the scratch will depend on the depth of the scratch. It is best to use the finest grit you can to grind out a scratch. I suggest starting with 2000 grit. If that is too slow, go to 1500 or 1200 grit and if it is still grinding too slowly, try 600 grit. However, after grinding with 600 grit, you will have to re-grind with 1200/1500 and then again with 2000 grit to remove scratches from the coarser grits. Only then, can the glass be polished with cerium oxide. NOTE: Grinding of glass can create an undesirable lens effect.
An easy way to grind out the scratches is to use silicon carbide sandpaper (the black sandpaper available at hardware stores or auto body shop supply houses) with water as a lubricant. After grinding, carefully clean off the area you ground with water and clean off your tools before going to the next finer grit. It's best to use an attachment on a drill, or an electric buffer.
Mix cerium oxide with water to create a slurry that's the same consistency as milk. Put the slurry on spinning buffing pad. Harder buffing pads made out of hard felt, or leather work best. The polishing action will be fastest when the cerium oxide is damp, but not dry, or runny wet. Fill a spray bottle with water and use it to keep the area you are polishing damp.
Glass is relatively easy to polish. Therefore, you don't need to use the more expensive 99.9% cerium. Instead, the less expensive 90% Optical grade will work fine. We have been told that 99.9% cerium works much faster than 90% on tempered glass.
Cerium oxide is now very difficult to get because of an embargo by China, the largest supplier in the world. The best substitute for cerium oxide is tin oxide, which is also now getting harder to come by. Unfortunately we are not able to provide any further advice on where to find either of these materials.