Want mirror finish on copper sheet

A. 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.

Q. 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,

A. 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 chamois ⇦[this on eBay or Amazon affil links] . 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.

A. Taking the finish to a 600 grit sandpaper followed with polishing using brown tripoli buffing compound ⇦this on eBay or Amazon [affil links] then by jeweler's rouge ⇦this on eBay or Amazon [affil links] 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.

A. 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 [a finishing.com supporting advertiser] 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,

Q. Hi John. I frankly don't know the answer to your problem myself. I'm wondering if anyone can comment on the possibility that your copper is simply too soft to be polished to a mirror finish (at least with the abrasives you are trying).

Regards,

A. Good day John.

We could use some more info regarding the copper you are trying to polish.
You state that your professional jeweler is stumped.
I am assuming you are dealing with a copper alloy as it relates to jewelry. It is quite possible there is a larger amount of other metallics within the copper- maybe zinc?
I would/have used a combination of muslin and fine cotton wheels (the muslin is very hard, providing the "cut" you need --maybe tripoli?-- to smooth out the surface, and finish off with the fine cotton with rouge with plenty of polishing rotation of the item to avoid heat generation = dragging/burning of the base metal = scratches-buff marks. (I like to use a hacksaw blade to "dress" the polishing wheels during polishing compound application, as it does help remove the fine buff marks/scratches).
Hope this helps.

Regards,

A. Mechanical systems as suggested will work; however, I am a lazy SOB. Polishing can be accomplished using vibratory systems and a dry organic polishing media. If your parts can fit inside the work chamber of the bowl it should polish up to a mirror finish. Scratches you may need to work with a wet plastic media.

A. To polish copper to mirror finish, I'm a Printmaker and often work with industrial copper which has to be polished to mirror finish.

Drop 20 weight oil drops on the copper and use 00000 #0000 steel wool ⇦this on eBay or Amazon [affil links] to remove the worst scratches, etc., than degrease the Plate and use 2000 grit from the car parts store wet sandpaper with water and go with the grain. A 24 x 30 inch Plate takes me about 90 minutes.

Ludwig