Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

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  for Metal Finishing since 1989
  

Painting marine compasses and boat/ship bronze & brass

Q. I do marine compass repair. Many marine compasses have a bronze "top ring" which seals the oil chamber. Frequently the top rings are tarnished or chipped --> they need repainting with a gloss black enamel. I've had much trouble getting a paint/primer to bond tightly to the bronze.

Things tried:
1) Krylon with and without primer
2) Hardhat with and without primer
3) Etching the clean bronze with ferric chloride
4) High % zinc primer

In all cases the problem occurs in the countersunk screw holes when the SS mach screws are torqued to proper ft-lbs. The paint tears away from the holes and surrounding surface. Much frustration! Here's hoping for some wisdom.

Note: I am NOT painting a bronze color - rather I need to paint black ONTO bronze.

Thanks in advance.

Brass Black Metal Finish on

eBay or

Amazon

(affil links)

A. Try an oxide solution. Birchwood Casey Company has a Black gel that you paint on with a brush [Brass Black on eBay or Amazon [affil links] . It turns the compass black with a process such as gun bluing. You need to rough the surface up a bit with a sand blaster or sandpaper to allow the oxide to bite.

Rich Darby
- Danville, Illinois
2005

A. I also repair compasses. That material is usually not bronze but naval brass (High zinc content). We continue to use Krylon with a primer. The key seems to be curing time. We do not get the problem if we allow a 24-hour cure before inserting fasteners. I have also used a dab of petrolatum in the holes on some jobs.

Bill Haimes
- Everett, Washington
July 16, 2009

Q. I'm not a professional finisher, but I do have a big boat with lots of bronze and I hate verdigris so it's a curse.

When polished I want bronze to stay polished and when painted I want it to stay painted - neither of which is easy.

First thing, nothing will stick to bronze tarnish - it has to be removed and I think preferably to at least a low polish state.

I don't believe any primers (etch or otherwise) will help, your finish coating has to go directly onto the metal.

For a black coating to handle mechanical stress, I think your choices boil down to: epoxy paint, powder coating, or electroplating with black chrome.

For a clear finish "Wattyl Paints" supply an aerosol spray specifically for copper that works on Bronze - (5 years in full sun before it starts to tarnish under the coating) - being a very hard coating, it may work as a primer under black paint - But I'd still use epoxy.

Thought of polishing the Bronze ring? very nautical look and the tarnishing problem will be tomorrow's problem for somebody else.

good luck