Metal finishing Q&As since 1989

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Metal Coating on Rock

I want to coat rock samples with some form of conductor, e.g., copper, silver, tin, lead. What would be the easiest and cheapest method. My reason is I want to test electric currents given off by some forms of rock like Basalt, and Granite.

Harold Lehamnn
At Home - Sarnia, ON, Canada
2005

Ed. note: Please start with our FAQ on this subject

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Hi Harold,
The best and very easy method to coat different kind of rocks, concrete etc., suitable for big parts of them, is metallisation (thermal spraying) using flame (for tin coating) or arc spraying gun (copper, silver). For good adhesion of the layer the zinc bond coat (20 - 30 micrometers) is necessary. Don't forget to remove any dust or grease from the surface prior to spraying.
Regards,

Piotr Milewski
- Warsaw, Poland
2005

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2005

Harold-
If your rocks are small enough, about 1x1x1/2 inch, they can fit into the sputter-coating machines used on samples about to be viewed by SEM (Secondary Electron Microscope). If you find one at a college nearby, and the owner will allow, it's fairly easy to run. They tend to be equipped with gold, palladium, nickel or chrome.

Easier ways are pure indium solder and a soldering iron, or painting on "DAG" carbon pastes and letting them dry. There is "AERO-DAG" in spray cans. There are copper, nickel, and silver pastes around too. Silver-epoxy was always our contact when we felt averse to heating the sample or using a vacuum machine. There are copper- and nickel-filled epoxies a little cheaper. For the small currents you will get out of rocks, perhaps anything will do. Even a water gel, such as used for medical tests like EKG's.

James Swenson
- Los Angeles, California, USA

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Best way is to spray silver paint on the dust free and dried rock.
Use powdered silver and mix it with thinner. If you get a granulated deposit, Silver is more in the spray liquid if you get miss deposit, add more silver powder.

T.K. Mohan
plating process supplier - Mumbai, India
2005