Removing Scraches From Your Glass Aquarium
by John T. Fitch
At some point, during the last few months, I managed to scratch the glass on the interior of our aquarium. It must have happened when I was cleaning algae off the glass. Because the scratches are roughly horizontal, I am reasonably sure they weren't made with the plastic razor blade I use, which is mounted in a notch at one end of a wooden dowel rod. That motion is almost exclusively up and down. The only other possible culprit is a "Cello" sponge, which I sometimes used to wipe off the algae film. That motion tends to be from side to side. And since it seems unlikely that the sponge itself could scratch the glass, I can only assume it must have picked up a piece of grit from the bottom or some other source, which was then pushed back and forth to produce these scratches.

You can't really see the scratches in the daylight, even with the aquarium light on. But, at night, they become sparklingly visible! Needless to say, I was very unhappy about what I had done and decided to see if there was any way I could get rid of the scratches. An e-mail to the manufacturer of the tank elicited a response that I could try buffing them out with "syrium"(!) oxide Are they syrious?

I then called a couple of auto glass shops and learned from one helpful manager that, yes, if the scratches aren't too deep, i.e. you can't feel them with your finger nail, you may be able to buff them out with cerium oxide.

So I turned to the Internet to find a source for this rare earth compound. It was soon apparent that it is used by jewelers and others to polish gems and stones. Cerium oxide is an extremely fine powder, though I don't know what there is about it that makes it suitable for this task. I did look up its toxicity, and decided it really shouldn't pose a problem for me or the fish. I found one source at www.facetingmachines.com, where I was able to buy a half pound quite inexpensively. Bob Kulakofsky, the owner, warned me, however, that it was going to take a lot of elbow grease. That was a real understatement!

When Bill, one of our sons-in-law, was here with his family for Christmas, I enlisted his experience (and muscles) to begin the buffing task. In the picture, you can see that we lowered the water level a little more than 50%, which was enough to get at the lowest scratch. We then floated a length of clear plastic wrap on the water and used masking tape to seal it against the glass to catch any drip or flying powder. In retrospect, we should have done a more thorough job of this, because some powder did get into the tank.

I had bought a hard rubber disk and buffing pad from Home Depot to mount on my electric drill, which, luckily, just fit inside the 12 inch width of the tank. We plugged the drill into a GFCI outlet. Then, as I mixed small batches of a slurry of cerium oxide and water, Bill started to work.

As you can see in this view from the kitchen side of our see-through tank, I had taken a blue Sharpie pen and marked the most obvious scratches (the white streaks are not scratches), so that I, standing in the kitchen, could guide his work. Well, after a solid hour of heavy pressure back and forth, it didn't look as though anything had changed. I was ready to call it quits, but after a short rest, Bill wanted to try one more time. And, lo and behold, after another fifteen minutes, many of the finer scratches were gone! Knowing now that the scratches could be eliminated, we decided to call it a day and try again later.

Now, in order not to mislead you, I have to confess that I didn't think to take a picture of the scratches before we started. The picture at the top of the page is of a very small section after we finished the first day's work. I've enhanced the picture somewhat; the scratches are not nearly as visible as they appear here. But we were reasonably confident that, with another hour of "elbow grease," we could eliminate the remaining scratches.

Before Bill and family came back for another visit, I had heard that silicone has the same index of refraction as glass and might be used to make the remaining scratches invisible. It was a lot easier than buffing and certainly worth a try.

Again, I lowered the water level about 50%. This picture shows Bill using the razor blade to spread a thin coat of aquarium silicone over the remaining scratches. We let it harden overnight and then carefully scraped off the excess. I raised the water level enough to cover the scratches, darkened the kitchen and living room, and we examined the scratches. They were still there! Whether the scratches were too fine to fill, or this silicone didn't have the right refractive index, I don't know. But the idea didn't work, and it was back to the cerium oxide method. Down went the water level again. We laid down a layer of clear plastic wrap, and this time were even more careful about taping it firmly to the glass. As result, virtually no powder got into the water.

After about another hour of hard work, we really couldn't see any scratches. This picture shows a small area of the glass, comparable in size to the picture at the top of the page. As you can see, the glass is really quite clear (except for the smears of slurry). So we cleaned up the mess and re-filled the tank. What faint scratches remain are really unnoticeable. I would call it a very successful project. That sponge, meanwhile, has gone into the dumpster! And, from now, I'll stick to the plastic razor blade.

I would be pleased to have your comments, questions, or suggestions addressed to: JTFitch@SpamCop.net . Thanks.

Photos were taken in December 2001 and January 2002, using a Nikon Coolpix 995 digital camera.