making new copper look aged green

I'm staggered that it took so long in the thread to come to this reply.

T'was bleedin obvious to me, though I do have a chemistry degree and have been involved in environmental pollution issues for many years.

Psst! Anyone got a can of tributyltin they don't want? I just want to keep the barnacles off the bottom of the boat!

On a related theme, have you noticed that increasingly it is impossible to buy any chemical product that actually *works*?

The easiest way is to keep the boat out of the water. Coincidentally this also means that you don't waste money on mooring fees, or harbour fees, or diesel. No sea sickness, torn sails, worn out engine, blocked toilet. Much reduced insurance fees are also a bonus.