Re: How to remove scratches from glass
I had door glass that apparently was left in the door in the rolled down position when the door was media blasted at some point earlier in it's life. The hole where the key cylinder was removed from in each door did a number on the glass about the size of a nickle (apparently the dummy that media blasted didn't think to cover the hole!). I ordered a cerium oxide polishing kit with a polishing pad that was about 6" in diameter but found it was way too large a diameter to remove glass damage like I had. Rather than give up, I tried a number of things and eventually came up with a process that worked very well. Believe me, the media blasted portion of the glass went far deeper than any scrape or scratch in glass I've ever seen. Both of my doors window glass had this problem, one of them I've done, the other I will soon do and will take photos with a step by step of the process and then post on this forum. Until then, here is a description of what I learned/did.
1. First off the cerium oxide by itself wasn't aggressive enough for my glass damage, so I purchased a small 2" or 3" diameter hard plastic disc with arbor that I could mount in my drill. Then I cut a number of sanding discs out of various grits of wet sand paper from 220 grit all the way up to 2000 grit. I attached the wet sand paper cut-outs (one at a time) to the plastic disc and arbor with masking tape rolled into 360 degree loops with the sticky side out.
2. I placed some damp sponges at the bottom of the glass along the top edge of the door where the felts are to create a barrier and absorb any water and sanding/polishing slurry that ran down the door glass while I was sanding and later polishing. Much easier to do this than to later deal with the mess that can get down into your door and on your felts. Remove these sponges every so often and rinse them in a pail of clean water. You could probably also use a towel folded the long way a few times if it would stay in place, the sponges worked out just fine.
3. I wet sanded the glass damage and moved progressively through each grit. The more coarse grits take less time to do their task, half the battle is determining when to move on to the next finer grit. Use a lot of water with a bit of detergent mixed in for lubrication and clean the glass often with a clean damp sponge. In my situation, I could see and feel the texture of the media blasted glass damage getting smoother. With each finer grit I moved to, I would sand a larger and larger area of the glass to make a feathered transition from the nickle sized blasting damage out to a larger diameter so the distortion in the glass would be less. Of course as the area being sanded gets larger and larger, the sanding does take longer and longer as you are covering a much bigger area.
4. Once you think you have sanded the glass all the way up to the 2000 grit and have the glass flat and smooth (relatively speaking), it's time to move on to the cerium oxide polishing. The best type of polishing pad to use with cerium oxide is a felt pad, but the one that came in my polishing kit was far too large a diameter for what I needed to do. I needed to be able to polish a smaller area like I had done with the power wet sanding. I purchased some some self adhesive 2" or 3" felt furniture feet and used them as buffing pads on the same hard plastic disc and arbor setup. They don't wear out very fast which was very surprising to me.
5. Mix the cerium oxide powder with water into a slurry, dampen the felt pad with some water first, then put a small amount of the cerium oxide slurry on the pad and start buffing the glass. It takes some speed and pressure of the buffing for the polishing to work best, if the glass and/or pad start to dry out, you either need more cerium oxide slurry on the pad/glass, or if there is still dried up cerium oxide on the pad, take a spray bottle of water and dampen the felt pad with it and even spray the glass in the area you are working. You don't want to polish so fast or use so much pressure that the glass gets hot. Feel the other side of the glass occasionally to see if it is getting hot and if so, modify your process to reduce the heat buildup.
6. You may find after using the cerium oxide and felt polishing pad for a while that the glass is still to rough and needs further wet sanding. This happened to me until I gained some experience and skills with the process. If this happens, just go back to the wet sanding operation for a bit longer and then move ahead with the process. I believe I had to go back and repeat grits 1000, 1500 & 2000 at least one or two extra times before the cerium oxide polishing gave me the results I was looking for. The 2000 grit you will need to use much more than the 1500 grit. Likewise the 1500 grit you will need to use much more than the 1000 grit, and so on down the various grits of paper. The 2000 grit by itself will polish the glass to some extent if you use it long enough, then the cerium oxide polishing finishes it off.
Notes: How course of a grit wet sand paper you begin with depends on the damage you are trying to repair. Experiment with a finer grit first and if it's not cutting the glass fast enough, step down to the next courser grit paper. I was able to get my first piece of glass so the original damaged area looks better then the rest of the original glass. It does take time and effort. I've polished everything from paint, to aluminum, and stainless trim. They are all much faster and easier to polish than glass is, glass is a really hard material. If you've tried polishing any of these surfaces in the past and decided you and polishing don't get along, you probably don't want to try and repair glass damage. But glass damage can be polished out with the proper materials, care, time and effort. Hopefully this helps anyone that really wants to remove damage from glass.
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