Copper and brass
Tarnish is the metal reacting with its surroundings, not dirt on top of it. Every polish that removes it removes metal too.
What not to do
Hydrochloric acid is unsafe on Copper and brass
Unsafe
Do not do this. The risk is established, and it is described below.
The reaction releases hydrogen, so this is a fire and explosion warning as well as a damage one.
Precautions
- Ventilate the area
- Wear gloves
- Wear eye protection
Evidence
Strongly supported
Sources
Right to Know Hazardous Substance Fact Sheet: Hydrogen Chloride (RTK 1012)
New Jersey Department of Health, 2016 · Government or regulator
Relied on for: That hydrogen chloride will attack many metals such as copper, brass and zinc to release flammable and explosive hydrogen gas. (states this directly)
Ammonia is unsafe on Copper and brass
Unsafe
Do not do this. The risk is established, and it is described below.
The regulator's instruction is written about equipment and generalises straightforwardly to a surface.
Precautions
- Ventilate the area
- Wear gloves
- Wear eye protection
Evidence
Strongly supported
Sources
Right to Know Hazardous Substance Fact Sheet: Ammonium Hydroxide (RTK 0103)
New Jersey Department of Health, 2011 · Government or regulator
Relied on for: That ammonium hydroxide reacts with heavy metals such as silver, copper, lead and zinc and their salts to form explosive compounds and flammable and explosive hydrogen gas, and that copper, aluminium and galvanised metals must not be used when handling it. (states this directly)
Acetic acid (vinegar) is unsafe on Copper and brass
Unsafe
Do not do this. The risk is established, and it is described below.
The sheet describes concentrated acetic acid; household vinegar is a few per cent. What transfers is the direction of the reaction, not its severity.
Precautions
- Ventilate the area
- Wear gloves
- Rinse thoroughly afterwards
Evidence
Strongly supported
Sources
Right to Know Hazardous Substance Fact Sheet: Acetic Acid (RTK 0004)
New Jersey Department of Health, 2016 · Government or regulator
Relied on for: That acetic acid attacks many metals forming flammable and explosive hydrogen gas. (states this directly)
Precautions
- Test on an inconspicuous area first
In detail
Copper and its alloys darken because the surface reacts with air, moisture and handling, and the patina is part of the metal rather than a deposit on it. There is no way to remove tarnish without removing metal, so polishing is subtractive and cumulative. The federal conservation procedure is correspondingly cautious, stating that copper alloy objects should usually not be polished at all, that where it is necessary the least abrasive approach is used, and that metal tools and commercial cleaners are excluded. It draws a distinction worth carrying into a kitchen: damage, including to the patina, cannot be addressed by cleaning — a corrosion mark or a scratch will not respond to more polishing, and continuing is how detail is lost. It also says these objects are not to be submerged and that liquid must not penetrate rims, edges or hollow parts such as handles — a real consideration for a pan with a rolled rim. A manufacturer adds the mechanical half: copper and bronze are durable but soft, and susceptible to denting and scratching. None of this says a domestic pan must be left dark. It says shine is spent metal, and the choice is worth making deliberately rather than monthly.
Properties
Sensitivity
- Acids
- Not known
- Alkalis
- Not known
- Chlorine bleach
- Not known
- Heat
- Not known
- Abrasion
- Sensitive
- Porous
- Not applicable
“Not known” means nobody has established this, not that the material is unaffected.
Related
- Copper and brass is commonly affected by Tarnish
Hacks and claims involving this
- Polishing brass and copper back to a shine Disputed
- Lemon and salt to clean copper Established practitioner practice
Sources for this page
Sources
Technical Procedures: Cleaning of Copper Alloy Objects
United States General Services Administration (GSA), Historic Preservation · Reference work
Relied on for: That copper alloy objects should usually not be polished, that where necessary the least abrasive approach is used, that metal tools and commercial cleaners are excluded, that objects are not submerged and liquid must not penetrate rims edges or hollow parts, and that damage including to the patina cannot be addressed by cleaning. (states this directly)
KALLISTA (Kohler Co.) · Manufacturer documentation
Relied on for: That copper and bronze are durable but soft metals susceptible to denting, scratching and scuffing, and that abrasive cleaners and solvents are not to be used. (states this directly)