Technical Briefs: Fire Stain on Brass

2 Minute Read

HomeLearning CenterJewelry MakingBench Tips and TricksTechnical Briefs: Fire Stain on Brass

Ganoksin may receive customer referral fees from the companies listed in this page.

By Tim McCreightMore from this author

Technical Briefs deals with technical concerns of interest to a wide audience, addressing topics as diverse as vanguard technology and ancient arts. It will also answer questions from readers and respond to suggestions, always trying to explain in simple terms the magic and wonder of working with metal. For this article, Tim will discuss fire stain on brass.


What You'll Need To Deal With Fire Stain On Brass

Buy List

Nitric Acid


Not available online
Sulfuric Acid


Sulfuric Acid Solution, 1.0M, 500mL - The Curated Chemical Collection
Get it on
Hydrochloric Acid


Hydrochloric Acid Solution, 2M, 500mL - The Curated Chemical Collection
Get it on


Sparex Granular Dry Acid Compoud No.2 10 oz.
Get it on

Bright Dip


Not available online

Sodium Bichromate


Not available online


Lortone 006-092 QT-66 Rotary Rock Tumbler
Get it on
Steel Tumbling Media


Stainless Steel Shot, Jeweler's Mix, 2 Pound Package
Get it on
Liquid Cleaner


Blitz 653 Gem & Jewelry Non-Toxic Cleaner Concentrate for use in Cleaning Machines, 8 Ounces, 2-Pack
Get it on
As an Amazon Associate, we earn from qualifying purchases referred from our site.

Fire Stain on Brass

Dear Tim,

I'm looking for help in removing a copper deposit that forms on brass and bronze alloys during pickling. I've been using either hand finishing by abrasion or bright-dipping, but both have their drawbacks. Is there something else I can try?

- Philip Smith, Norristown, PA

Dear Philip,

Your problem is basic to copper alloys. At high temperatures copper and its alloys combine with oxygen to make several oxides, the most important being cuprous oxide and zinc oxide. The latter is an easily dissolved film that comes off in just about any subsequent rinse. If the work is pickled in a mild sulphuric solution (like Sparex #2) the copper oxide is reduced to pure copper. This is the pink-orange film you're finding on your work. As you might have noticed, increased temperature will create a thicker layer of copper Polished surfaces will oxidize more slowly than rough ones.

Most commercial solutions to this problem rely on bright-dipping, or a quick bath in acid to attack and dissolve the copper. Typical solutions use (by volume) 25% nitric acid, 60% sulfuric acid and a trace of hydrochloric acid. These are generally used at room temperature. Parts are dipped in pickle, rinsed, dipped in bright dip, rinsed and thoroughly cleaned. In a factory setting that deals with a single alloy and repeats steps with great regularity it's possible through experimentation to arrive at a concentration of bright dip and a system of application that will give consistently excellent results. For the studio craftsman who works with several alloys and whose line involves diverse work, the process is less satisfactory. The additional hazard of this super-strong acid is enough drawback to make many people shy away from bright-dipping.

A less common and somewhat safer pickle specifically for copper and brass can be made of:

  • Concentrated sulfuric acid, 4-10% by volume
  • Sodium bichromate, 4-8 oz. per gallon

Water, remainder Ferric sulfate may be substituted for sodium bichromate in the above recipe, at the rate of 10-25 oz. per gallon After a standard soaking in Sparex, rinse the work and immerse it in this solution at room temperature. The duration of the soak will depend on the depth of the copper stain. Alter removing from this second pickle, wash the metal thoroughly with soapy water.

If abrasion is the route to go, your next thought would be to investigate tumble (also called barrel) finishing. One choice will be vibratory polishing, a process in which abrasive-packed plastic or ceramic pieces are cascaded over the work. This is quite last, easy and versatile. The alternate choice is tumble finishing, in which the work is packed into a sealed drum along with steel media and a liquid cleaner. The drum is rotated by machine, tumbling the work over and against the media. This is slower but permits the use of heavy material like steel. These burnish and work-harden simultaneously.

Send questions for this column (double-spaced, typewritten) to:

Tim McCreight
23 Mill Road Circle
Boylston, MA 01505.

By Tim McCreight
Metalsmith Magazine – 1985 Summer
In association with SNAG‘s
Metalsmith magazine, founded in 1980, is an award winning publication and the only magazine in America devoted to the metal arts.

You assume all responsibility and risk for the use of the safety resources available on or through this web page. The International Gem Society LLC does not assume any liability for the materials, information and opinions provided on, or available through, this web page. No advice or information provided by this website shall create any warranty. Reliance on such advice, information or the content of this web page is solely at your own risk, including without limitation any safety guidelines, resources or precautions, or any other information related to safety that may be available on or through this web page. The International Gem Society LLC disclaims any liability for injury, death or damages resulting from the use thereof.

Tim McCreight

The All-In-One Jewelry Making Solution At Your Fingertips

When you join the Ganoksin community, you get the tools you need to take your work to the next level.

Become a Member

Trusted Jewelry Making Information & Techniques

Sign up to receive the latest articles, techniques, and inspirations with our free newsletter.