No registration, no passwords; no pop-up ads -- just aloha, fun, & authoritative answers.
As an eBay Partner & Amazon Affiliate we receive compensation for qualifying purchases.
Home /
Search 🔍
the Site
pub  Where the world gathers for
plating, anodizing, & finishing Q&As since 1989


Green Tarnish on Copper Courthouse Dome

We are cleaning our copper dome on top of the courthouse. We have had good success at removing two coats of old paint using just plain paint stripper. Under the paint is that old green tarnish. In testing, muriatic acid [affil link] seems to remove this green tarnish very well. But muriatic acid is very dangerous. Any recommendations on how to remove this green tarnish more safely? How do we keep this green tarnish from returning too quickly? All suggestions and comments are welcomed. Thanks Butch Bridges.

Butch Bridges
Carter County Courthouse - Ardmore, Oklahoma

Wow. You've got a tough one there. You're absolutely correct that Muriatic (Hydrochloric) Acid is very effective at removing the tarnish. The problem is that copper is such an active metal that it forms oxides very quickly. I am not aware of any practical or cost effective method that will inhibit the tarnishing process on such a large scale.

I work with copper plated parts every day and anything short of lacquering or chromating the part do you have a chance of inhibiting the tarnishing process. The green patina that you see on copper is a naturally occurring chemical process that will occur unless you apply a film or barrier over the copper. Many people find this patina film to be an enhancement to the that has occurred over the years. Unfortunately, if you like bright, shiny copper; you must protect the polished surface immediately or the tarnishing will occur very quickly.

On anything as large as a building dome the only alternative I would see would be an organic coating of some sort. It would be extremely impractical and environmentally hazardous to attempt this. My advice is to clean up the copper as well as you can so you can see the copper color for a short period of time but you can be assured that the patina will return. Good luck to you.

Daryl Spindler
Daryl Spindler, CEF
decorative nickel-chrome plating - Greenbrier, Tennessee

They grit blasted copper with sodium bicarbonate to clean the Statue of Liberty. Commercial units are available. Don Mattox

Donald M. Mattox
Society of Vacuum Coaters
Albuquerque, New Mexico
Donald is the author of: Handbook of Physical Vapor Deposition (PVD) Processing and The Foundations of Vacuum Coating Technology [affil links]

I want to make the green tarnish on copper for crafting. Any ideas on a quick method? or just leave the copper out in the weather for a while? Thanks for any tips.

Connie Simmons
- Raymond, Mississippi

(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

Chemicals &
Consult'g, Train'g
& Software

About/Contact  -  Privacy Policy  -  ©1995-2024, Pine Beach, New Jersey, USA  -  about "affil links"