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"Bluing or blackening brass"

Current question and answers:

December 31, 2020

Q. Hi,

Do you have any experience with Patinas on brass? We use a patina (blue type solution), it's patinating purple not brown. Would you know why?

Cheers Daniel

Daniel da costa
- Melbourne NSW

January 2021

A. Hi Daniel. Not knowing what you are trying to patinate, what chemicals you are using for it, what method you're using (dip, spray, brush), and whether you have never succeeded before or you've been doing fine for years and this problem suddenly popped up, it hard to suggest much ...

But the purple color can be one of three things, a contaminant which produces a purple salt (and that sounds unlikely); a very thin patina which lets the Yellowish brass color enter into the equation, producing purple from yellow & blue; or a thin patina that is introducing a diffraction/interference coloration (a color which isn't really there as a pigment of any sort).

Please take your purple item and just patinate it a second time, and tell us what happens. I think it will turn brown. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Previous closely related Q&A's, oldest first:


Q. I need to find a recipe for a brass blackening solution.

What I've been trying so far is:

copper nitrate [affil. link to info/product on Amazon] in distilled water and equal quantity of ammonia + sodium carbonate (washing soda) [affil. link to info/product on Amazon] to reduce the acidity.

This solution should take about 1 minute to produce rich "Gun-blue" black on brass, but it doesn't work properly. Thanks for your help.

Massimiliano C [last name deleted for privacy by Editor]
Australian National University, Canberra, ACT-AUSTRALIA


A. There is a plating process which requires copper plating followed by blackening in a solution called Ebonal. I cannot remember the particular supplier. Good luck.

Jeff Mills
metal finishing shop - Gorham, Maine


? Have you tried Electroblack?

It's available in Australia from Macdermid.

Mick Long
- Australia


Q. I am trying to reproduce a blued finish on the brass boilers of a collection of antique model steam engines, most made in Nuremburg, Germany between 1870 and 1930. The finish on these engines range from purple to brown to dark blue. These can be seen at: http://John_o.myiglou.com/steammain.html

So far, commercial firearms bluing solutions have gone almost straight from brown to blue. I have heard that the old builders used a salt solution heated to the 80-90 degree (c) range to achieve this finish, but can find no documentation on this method, or the materials used. Can anyone point me to good reference material on this, or shed some light on the solutions used to achieve this finish?

John O'Rear
- Versailles, Kentucky, USA


A. Lustre colours solution:
lead acetate [affil. link to info/product on Amazon].......25 gm
sodium thiosulphate [affil. link to info/product on Amazon]...240 gm
potassium hydrogen tartrate (cream of tartar) [affil. link to info/product on Amazon]....25 gm
H2O..........1 lit

/ for copper and its alloys,iron(only blue), silver, gold, platinum, nickel plate/ Solution produces a series of lustre colours in following sequence(on brass): golden yellow-orange-purple-blue-pale blue-pale grey(cca 10 min.for sequence,40 °C temp.)!

Goran Budija
- Zagreb, Croatia

To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)


Q. I am the head of Quality Dept. co project cum customer service in my company. The line of business of the company I'm with is in Metal Surface Treatment. Currently we are doing a type of surface treatment called bluing on brass parts. And the parts and components are for microscopic surgery use. My company uses Ammonium Nitrate and copper carbonate [affil. link to info/product on Amazon] for the bluing process.

My question is how do we strip or rework brass parts (already blue but not cosmetic accepted) or re - blue them again. Knowing the brass is a sensitive material. We have tried some test of stripping it with acids (nitric, sulfuric) but instead it oxidizes or corrodes the brass components. Have any suggestions that we can try out?

Gerald Cornelius Federick
metal surface treatment - Johor Bahru, Johor, Malaysia


A. Sanding, both dry and wet is the only way I've heard to strip brass w/o oxidation. start w/ 1000 grit and work up to 1500/2000. very labor intensive.

Thomas Wheeler
- Dallas, Texas

To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)

Bluing or blackening miniature cannons


Q. I would like to find out a way to black or blue miniature cannons. These cannons are part of a model ship that I am building. The cannons are made of brass, and I would like to make them look more realistic.

Oscar Allen English
hobbyist - Lakemont, Georgia, USA


A. Pre Civil War, many cannons were made of brass as that metallurgy was fairly well known, Cast iron cannons had problems, mostly from casting problems. So, black cannons did not really come into mass production until steel was made around 1860. Parks paint theirs black, so they do not have to polish them. That said, spray paint of a desirable gloss would be the quickest and cheapest. Hold the can about 2 feet away from the cannons and do not attempt to get complete coverage at one time. think two coats on the top and two coats on the bottom side.

James Watts
- Navarre, Florida


A. Black patina for brass:

200 grams copper carbonate [affil. link to info/product on Amazon]
1 lit ammonia (25%)
Cold immersion! Very bad smelling but very effective solution!

Good luck!

Goran Budija
- Zagreb, Croatia

"The Colouring, Bronzing and Patination of Metals"
by Hughes & Rowe
from Abe Books

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Q. Hi,
I need tips on readily available solutions/gels, etc. for browning/blacking/bluing brass details please (from light brown to dark brown, black and gun blue)? Must provide reliable predictable and durable results. Or if there is a collection of well tried "recipes" available (a book, etc.) -- info on that would be most welcome? We are building fine mechanical designs.
Any help is gracefully received - thanks.

Peter Sisask
Manufacturer - Stockholm, Sweden


A. What are the parts which you are asking for?
are they too large?
are they stored in the place were their is moisture?
is Oxidation the problem?
Brownish discoloration or a bluish patina which is coming over a period of time?
I feel if it so I have the answer for that.

Please confirm my above questions first!


Sachin Pareek
- Vasco-da-gama, Goa, India

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