How to polish a copper sheet?

[reaction]

Hello everybody,

I am not very good in metals so I need you experience how to polish an 1 mm thick copper sheet with light cracks and oxidation. I don't want to have a mirror-like look - just a beautiful and machine-like mat look will be ok for me. I will use the sheet as a top pannel in my current tube amp project.

Thanks in advance.

[tiroth]

I usually start with coarse steel wool and just keep going until I get the finish I want. If there is really bad oxidation, maybe some 220 or higher grit sandpaper first.

The key is keep your strokes long and straight...preferably begin and end each stroke off the surface. And wear a dustmask!

[rcavictim]

You can save a lot of polishing and reduce the amount of metal removed in the process by first washing it clean with muriatic acid, AKA HCl or Hydrochloric acid. This is available at the hardware store for etching concrete and cleaning coffee makers really well (once you discover that CLR is overpriced and totall next to useless). It comes in about 35% strength and will smoke when exposed to air. Wear rubber kitchen gloves and don't breathe the fumes. Do not do this indoors as the fumes will corrode other stuff in the house/shop. Great also for brass. Can be used straight for really tough corrosion or diluted 50%. After the acid dip rinse well with tap water. Now you should be ready for fine steel wool. I would use #0000 wool and then rub with a soft cloth and Brasso for a fine polish. The Brasso leaves a coating (like a wax) that helps prevent oxidation for a while.

BTW, for coffee makers pour about 1- 2 ounces into the hopper half filled with tap water, then fill the rest of the way with water. Several rinse cycles (like you are making coffee without the coffee) are suggested.

[thomas997]

Originally posted by tiroth
I usually start with coarse steel wool and just keep going until I get the finish I want. If there is really bad oxidation, maybe some 220 or higher grit sandpaper first.

The key is keep your strokes long and straight...preferably begin and end each stroke off the surface. And wear a dustmask!

hm I read this on another site:

"I do *NOT* use REAL *steel* wool, since it WOULD cause RUST/oxidation, after it's embedded in the copper."

[tiroth]

It isn't true. I have processed tons of copper using steel wool, final wash with acetone, and it does not oxidize. Some kind of clearcoat is needed for a permanent finish, but I prefer not to use one where possible. The downside is the finish may need a little maintenance in a few years, or sooner if fingerprints are a possibility.

[Lisandro_P]

Copper will oxidize with time. I've built a small headphone amp with a copper front (see here), and had to cover the front with a tiny layer of clear laquer.

After a couple weeks, it was evident it was a good idea; the unfinished back size oxidized pretty fast.

[tiroth]

Copper WILL oxidize of course, although if you are in a low-pollution environment you can get by without a coating as long as you are willing to do some light polishing once a year or so. This means zero fingerprints allowed though!

What I meant was, there is nothing wrong with using steel wool. It won't cause "rust."

I like the amp Lisandro.

[Lisandro_P]

Thank you tiroth!