I sell marine bronze valves made from China.. So, I have seen this type of situation before. There are few reasons this happens (as explained by factory) which is due to oxidation, which i don't believe, as it only happens on some of my valves and only on specific sizes of valve and specific batches.
So, what we did, is using sand paper to rub it off, some works, mostly doesn't, and some are very deep into the material, so it is impossible to remove, even those removed, may re-appear.
This made us believe that this is due to material contamination (which is another factory given reason, to avoid responsibility) and/or bad mixture of material, because bronze is not 100% cooper, rather a mixture of mainly Cu (cooper), then Zn (Zinc) and little Pb (Lead) and Fe (Iron). So, too much Pb and Fe or bad "cooking' process will cause this to happen and it will not go away, bcoz you can't remove Pb and Fe from the mixture. Unless you grind it off.
We also tried paint thinner, it only works if the greenie thingy is on the surface not deep down.
I tried to find pictures, will show when i find it..
This is why when i hear pam 382 bronzo was released, i didn't get too excited bcoz i was worried this may happen..
Update: i asked my worker what happened to those valves in the end, they were all sold, customer didn't complain much because when those valves are in operation (at sea), salt water will speed up this process and looks much worse than what we initial had. Usage wise, no effect.
So, what we did, is using sand paper to rub it off, some works, mostly doesn't, and some are very deep into the material, so it is impossible to remove, even those removed, may re-appear.
This made us believe that this is due to material contamination (which is another factory given reason, to avoid responsibility) and/or bad mixture of material, because bronze is not 100% cooper, rather a mixture of mainly Cu (cooper), then Zn (Zinc) and little Pb (Lead) and Fe (Iron). So, too much Pb and Fe or bad "cooking' process will cause this to happen and it will not go away, bcoz you can't remove Pb and Fe from the mixture. Unless you grind it off.
We also tried paint thinner, it only works if the greenie thingy is on the surface not deep down.
I tried to find pictures, will show when i find it..
This is why when i hear pam 382 bronzo was released, i didn't get too excited bcoz i was worried this may happen..
Update: i asked my worker what happened to those valves in the end, they were all sold, customer didn't complain much because when those valves are in operation (at sea), salt water will speed up this process and looks much worse than what we initial had. Usage wise, no effect.
