Metal finishing Q&As since 1989

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How to do blue coloring on cast aluminum

I am making 6' aluminum castings of blue Herons and would like to color them w/ blue and black. I know they can be dipped commercially, but want to do them by hand to achieve better effect. We are sculptors (and stone masons) who work in metals, stone and wood. These are cast in the "lost foam" method.

Thank you,

Kenton Pies
- Gold Bar, Washington, USA
2003

A. Hi Kenton. The castings can be brush anodized and dyed, I believe. Any time you are working with castings there will be impurities that make clear anodizing difficult or impossible, but as long as you're looking for a dark blue-black, I anticipate that you can anodize and dye them. Warning, though, there's a lot of steps and labor! Talk to a supplier of brush plating equipment.

But before you do, try the simple idea of a permanent marker. They work pretty well on aluminum.

Regards

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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2003

A. Your castings can be chemically oxidized and dyed:

Chemical oxidizing:
2-5% sodium carbonate / washing soda [affil links]
0,5-2,5% potassium chromate
1 lit. water
90-100 °C, 3-5 min(for 100 dm2)

Hot immersion( only grease free objects)! Thoroughly rinse and then dye!

Blue dye for aluminum (2 step process):
SOLUTION 1- 50 gm. iron(III) sulphate,1 lit. water,50 °C temp.
SOLUTION 2- 25 GM potassium ferro(II)cyanide, 1 lit. water, 50 °C.

Immerse object in solution 1 (2-10 sec.), thoroughly rinse and then immerse in solution 2, rinse again and dry and lacquer object. Instead immersion solution may be sprayed or brushed.

Goran Budija
- Cerovski vrh Croatia