Ask A Scientist Chemistry Archive

name         Necia L.
age          60s

Question -   During remodeling this year, I used copper as a facing for cupboard and drawer 
fronts. Before inserting the copper, I burned it, making it glow several shades of beautiful 
red, some blues, and several hues in between. It was really glorious. BUT I didn't seal the 
copper. Now all the cupboards and drawers have been in place for several months and I find 
that every drop of everything that has touched them has left a sloppy looking mark. I know 
I can clean it with copper cleaner, but that will remove the beautiful reds. I can't heat 
them up again because they are framed in wood, which will combust at that temp.
Is there anything I can do to clean the spots off the copper and retain the color?
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Necia,

It was a chemical; reaction that produced the beautiful colors. Likewise, a chemical 
reaction produced the stains. Now they are part of the copper surface and they cannot be 
removed without damaging the underlying metal and surrounding area. I think the only 
alternative is to start over. Remove the metal from the frames, clean it, repeat the 
heat-treatment and then seal the surface before reinstalling it. You have learned a 
painful lesson in not having sealed the original surface.

Regards,
ProfHoff 743
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This can be tricky!!! The 'heat treatment' you gave the copper formed various copper oxides 
of differing film thickness(es) on the surface. I would not recommend a copper "cleaner" -- 
at least not to start with because the "chemistry" of most of those cleaners involves 
complexing the copper in the oxide film to REMOVE the oxide film -- and that is not what 
you want to do. What you want to do is remove the "spots". Now if the "spots" contained 
ammonia they will not be removed because the oxide film will have been damaged. However, 
if the oxide film, which is porous, has just absorbed some of the staining material, you 
might try a very mild abrasive cleaner. An old standby for cleaning brass is a product 
"Bon Ami" that you can find in the grocery store or hardware store.
Of course try a small area in an inconspicuous spot to test this, or any, treatment. You 
might also ask a friendly jeweler what (s)he might recommend. There may be something 'out 
there' formulated to do exactly what you want.
If you are successful, then seal the copper with a clear acrylic urethane that will prevent 
further staining. Of course here you have to be careful to select one that has the gloss 
and/or sheen you may wish to preserve.

Vince Calder
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