Scientific American 21, 23.5.1863
Steamships composed mostly of iron, and covered merely with iron plating on wood, are fast superseding entire wooden vessels for mercantile and war purposes. But iron vessels are defective in one important point. When in service for a comparatively short period of time, their bottoms become covered with weeds and barnacles to such an extent as to cause great resistance to their progress through the water, and a considerable loss in their speed is the consequence; this amounts to about one mile per hour, during every month they are in service, hence they require to be frequently put into dock for the purpose of cleaning and painting them. It is stated by men of experience in such matters, that when iron vessels enter warm-fresh-water rivers, all the shell-fish which may have been adhering to them drop ooff and their bottoms become quite clean. But as most shipping ports are situated in bays of salt water, this fact affords no great comfort to the prorietors of iron ships. The great object for such vessels has been to obtain some composition, like a paint, which, when applied to them, would exert no chemical action upon the metal, and yet would be as effectual as copper sheating on wooden vessels, in keeping their bottoms free from shell-fish and seaweed. Red lead is the common paint used for iron steamers, but it is not a very efficient protective, and many other paints and compositions have been tried, but hitherto with no very gratifying success, so far as we know. A composition has at last been discovered, which, it is said, answers all the requirements. At the general meeting of the Institute of Naval Architects, lately held in London, W J. Hay, professor of chemistry in the Royal Naval College, Portsmouth, England, described the paint, and related that it had been tried with other compositions since 1857. It consists of the oxide of copper boiled in linseed oil. A sub-oxide of copper is roasted until it has absorbed sufficient oxygen to become black oxide; then it is reduced to powder and boiled in linseed oil until it assumes a puce color. It should be of moderate thickness when applied. The armor-clad frigate, Warrior, was coated with this paint, and after she had been nine months in service, Professor Hay stated that, when docked, no signs of oxidation were obser[v]able in her plating, and her bottom was comparatively clean.