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"Blackening zamak and zinc castings to antique look"

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An ongoing discussion beginning back in 1996 ...

1996

Q. Dear sir,

Is it possible to apply a black chromate directly onto a zinc die-casting without zinc plating the part first? Although it sounds logical, I have not been able to make this work.

Keith Rosenblum
plating shop - St. Paul, Minnesota

2001

A. Mr. Rosenblum,

Black chromating is difficult to produce on zinc castings, but there has been research performed by Ilzro on this matter.

Ryan Winter
- Maybrook, New York

Ultrex Z 27

2001

Q. We are currently experimenting with Ultrex Z-27, a chemical to blacken Zinc Diecastings. I was wondering if anyone has had any experience with this and if so what problems did you encounter?

Bob Lehenbauer
- Monroe City, Missouri USA

Hi Bob. We don't really like to discuss proprietary products here (why?).

But in general terms, it's a lot easier to consistently & aesthetically blacken zinc plating than diecastings -- which may have cold shuts, porosity, inclusions, and other materials (like varying amounts of aluminum). I think this situation of difficulty with castings persists regardless of what brand or type of chemical blackening you use. Iridescent yellow chromating, where less consistency is inherent and expected, may be more achievable.

Regards,

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

Blackening Zamak KS

2004

Q. Hi

I have just transferred to casting zamak ks I am casting in centrifuge {used to cast pewter}.

I am having a problem blackening zamak ks for antique look -- don't know which blackener to use.

Please help ?

Efi Maya
casting - Telaviv, Israel

2004

A. You can use 200 gm iron chloride/1 lit water solution (cold immersion, up to 20 minutes). 12 gm copper sulphate/15 gm potassium permanganate/1 lit water solution (90 °C) solution works too.

Good luck!

Goran Budija
- Cerovski vrh Croatia

Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)

2004

Q. I have acquired an antique lamp with glass panel and cast zinc frame. The zinc casting appears to be bare metal, oxidized to a faintly greenish grey over many years. Many of the similar lamps which I see have a dark, usually black, color to the zinc, which does not appear to be an applied coating like paint or lacquer. I would like to know how that surface color was achieved; was it a metal plating process, a chemical conversion similar to blueing, or some other method. If the process can be produced at home safely I expect to try it, but I do not intend to get into metal plating.

Chris Paine
hobbyist - Pasadena, California, USA

2004

A. You can use 200 gm iron chloride/ 1 lit water solution! Your object must be grease and oxide free!

Good luck!

Goran Budija
- Zagreb , Croatia

2004

Q. Hi Goran,

So just to clarify, the formula is 200 grams of iron chloride with 1 liter of water. The process is cold immersion for 20 minutes. You say it should be free from grease. Do you think I can use the same cleaner/degreaser for zinc as I use for my copper sheeting?

Deanna Rich
- El Segundo, California, USA

Black Patina for Zinc

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A. Hi, Deanna

It's hard to say whether your cleaner/degreaser is safe for zinc if we don't know what it is. Most solvents are harmless to almost all metals, but caustic based cleaners may be too strong for zinc.

Rarely can you use a single batch of solution for two different purposes because of side reactions. So if you use an acidic solution like ferric chloride on copper, copper will become dissolved into it; then if you use it on zinc, the copper will immersion plate onto the zinc in the fashion of the familiar school lab where iron nails become covered with copper if placed in a copper sulphate solution. So it's best to maintain separate solutions for treating zinc and copper. Good luck.

Regards,

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

December 14, 2014

Q. Could you please tell me the instruction for blackening zamak -- I need the resistance blackening!
Thanks.

hossein aghaie
- qazvin, Iran

December 2014

A. Hi Hossein. We appended your inquiry to a thread which hopefully at least partially answers it. But I don't know what you mean by "resistance blackening" ... can you try some different words?

Regards,

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

Zamac 5 or 3 Post Machining Blackening

May 11, 2020

Q. We are buying a Zamac 3 or 5 casting that we are machining. We would like to blacken these after machining to match a black anodized part. What process will help us get there?
Thanks,
Tim

Tim McNabola
- Wallingford [PA? CT?]

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