About Tarnished Brass

Brass is actually a combination of two metals: copper and zinc. Composition of brass can vary anywhere between 95 to 55 percent copper (5 to 45 percent zinc). If brass is not lacquered, the metal gets exposed to air which causes it to oxidize or tarnish.

Appearance

Tarnishing occurs when brass is exposed to air.

Tarnished brass has a dull finish and a patina (coating of copper sulfide) that starts out brown, but eventually turns black. Outdoors, where brass regularly gets washed by rainwater, the copper sulfide will appear blue-green in color.

Function

Tarnish can actually protect brass that is outdoors.

Tarnished brass is not always a bad thing. Some consider a little tarnish desirable, especially on antiques. Older brass items should always be cleaned by professionals to avoid damaging the piece. Natural corrosion patina (tarnish) will actually protect brass that is outdoors from corroding further. However, it will only work if the patina is formed uniformly and it adheres to the brass tightly. Unfortunately, rainwater can mix with chemicals that wash away the patina, which will cause the metal to corrode further.

Removing Tarnish From Small Items

You can remove tarnish from small items by boiling them in vinegar.

When you remove tarnish from brass, you are actually removing a thin layer of the brass. This can be very difficult to do by hand. If it is solid brass and small, try boiling it in vinegar, which will turn the brass a reddish color that can be removed by polishing with a soft cloth.

Removing - Large Items

Antique items should only be cleaned by a professional.

Remove tarnish from larger items by washing the item with hot water and weak ammonia or soapy water. Rinse well. Then, heat up some vinegar. Dip a cloth into the vinegar and then some salt. Rub the vinegar and salt onto the brass. An alternative is to make a paste using salt and vinegar and leaving it on the brass for an hour before removing.

Prevention

Keep brass from tarnishing by wiping it with ammonia.

You can prevent non-lacquered brass from tarnishing by wiping it with a soft cloth and liquid ammonia once a week. You can also coat your brass with brass lacquer. However, the lacquer can become scratched. When this occurs, the metal underneath will tarnish and leave a black line on your item.

Resources

• Metals in America's Historic Buildings
• Cleaning Brass - Care and Repair
• Cleaning Brass the Professional Way