Recommendations on Bronze Discoloration?

[John Stone]

I have a lot of external bronze on the Far Reach. We do not polish it. Not all of it is the same kind though—silicon bronze, aluminum bronze, manganese bronze, and some “other.” The bronze hardware we made is all silicon bronze—bulwark brackets, outboard mounts, brackets for kerosene nav lights, etc. All of it has turned a beautiful blue-green. The aluminum bronze used to cast our gammon iron by PTF has not turned green just slightly dulled. The manganese bronze chain plates seem to have remained mostly unchanged as well.

But a few pieces of bronze have gained an ugly black coating. I don’t know what it is. It seems to associated with the less expensive hardware—some old ABI bronze padeyes and one spartan Marine chain pipe cover for our stern anchor—photos below. It seems resistive to scribbing. I used a maroon 3M pad on it to test if that would have any effect. It had no effect though I did not rub hard or for long.

In the vast repository of knowledge in the Cape Dory Brain Trust (CDBT), does anyone know:
1. What it is?
2. How to remove it without removing the hardware or damaging the Awlgrip?
3. How to prevent it in the future?

Thoughts and suggestions (short of keeping it polished- ) are appreciated.

[Jim Walsh]

I have the same variations in color. Some pieces of hardware are a beautiful verdigris color. I just attributed it to variations in the alloys used to produce the bronze. The verdigris color is the result of the formation of calcium carbonate on the surfaces.
I'm just thankful for so much quality bronze hardware on our boats.

[tjr818]

In my limited experience there are two ways to get the bronze to turn green. The easiest and least expensive way is Time, lots of Time. The other way is to hasten the patina chemically with something like these:
https://sculptnouveau.com/collections/t ... en-patinas

[noreaster]

Off topic, but is your non-skid kiwi grip?

[John Stone]

Yes. It’s kiwi grip. Not as durable as interdeck or similar products but easy to work with and super easy to touch up. Also easy to customize the aggressiveness of the non skid. Highly recommended. It’s been under the sun for three years. Looks good but we have touched it up.

Here is a link to the documentation of our application of kiwi-grip. Scroll to near the bottom to find the entry.

http://www.farreachvoyages.com/projects ... erior.html

[noreaster]

Yes. It’s kiwi grip. Not as durable as interdeck or similar products but easy to work with and super easy to touch up. Also easy to customize the aggressiveness of the non skid. Highly recommended. It’s been under the sun for three years. Looks good but we have touched it up.

Here is a link to the documentation of our application of kiwi-grip. Scroll to near the bottom to find the entry.

http://www.farreachvoyages.com/projects ... erior.html

Thanks so much! It looked like kiwi grip, but not as aggressive of a pattern.

[John Stone]

I could make it more aggressive but it seems to work well when minimal stipple. I prefer to sail barefoot when I can and it works works well that way. I’ve seen it applied so aggressive you can’t sit on it without a cushion. Didn't want that.