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Want mirror finish on copper sheet

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I am creating bookmarks and other curio items from 20-32 gauge copper sheet materials. My objective is to obtain the best "mirror" or "plate" finish on the completed items. I have used 600 Grit sandpaper and handheld polishing tools but cannot remove scratches.

Eladyah Jones
hobbyist - WESTFIELD, Pennsylvania


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Well, you have to get those scratches out, and you can't do it without ruining the shine and starting over. Sorry, Eladyah. What you need to do is use a coarse enough sandpaper to get every one of the original scratches out, leaving new scratches perpendicular to the original ones and somewhat smaller and less deep. Then you need to use a finer sandpaper and get all the scratches out that you just created, replacing them with smaller and less deep scratches in a perpendicular direction. You keep doing this with however many steps are required; the minute you leave a prior scratch behind, you've lost the battle and there is no sense continuing. Unfortunately, you simply have to get all the scratches from the previous step out before you can go on.

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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Ted,

I have now attempted to finish two additional samples of the copper sheet. Unsuccessfully. I followed your instructions carefully and even though I used several grits of paper, I was never really able to get the desired finish. On the latest attempt, a "sort of" mirror finish appeared. On this sample (1"x4"- 20 Ga) as with the earlier one, the last size of paper leaves scratch marks of its' own. I went to 2000 grit emery with this last try.

Should I try some kind of polishing compound ? Or would using the emery under water help ? I'm still looking for a way to do this.

Regards,

Eladyah Jones (returning)
hobbyist - WESTFIELD, Pennsylvania


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There are various grades of a 3M product called scotchbright, one of them is so aggressive I think it has diamond grit in it. They work really well wet with water. Use a fine cutting compound 4,000 meshed size that is about the finest grade you will get. apply it with low linting paper towel or a Chamoisamazoninfo. Always use cold water as hot rapidly causes the copper to tarnish finish with a rinse in deionized water then displace the water with metholated spirits.

Robert Fyfe
- Wyoming, NSW, Australia


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Taking the finish to a 600 grit sandpaper followed with polishing using tripoli [link to product info at Amazon by ed.] then by red jeweler's rougeamazoninfo will give you a mirror finish. Use a bench polisher and muslin buffs.

Or, if you have a (rock) tumbler, you could use steel shot and tumble your items after the 600 grit sandpaper step.

Both methods will give you a mirror finish.

Cheryl Bdeleted
- Shrewsbury, Massachusetts

Rock Tumbler


December 21, 2011

Q. I have made some copper post caps (10"). Various angles and seams make it hard to polish? I did some sand blasting on parts of them; leaves it very clean w/sparkling glitter-like look in the proper light but kind of a matte finish in different light? Definitely the easiest way to clean it what next?

jim pettis
- anderson Ca USA

December 22, 2011

Hi, Jim.

Sandblasting has removed the oxides and discoloration, which is why it looks bright in one way. But it has imparted a wavy, pockmarked profile -- which is why it looks matte in a different light. You won't get to a mirror polish by blasting, but if you are almost happy with what you have, some improvement may be possible with a clear coat. Wet the copper with water. If you like the way it looks when wet, a clearcoat like Everbrite can probably give you pretty much that look.

If you don't like it even when wet, you are not going to get the look you like without changing your approach from blasting to buffing. Good luck!

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
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