There are four patents, in which various, so-called, non-conducting coats are put on the iron, and copper pigment in some form put on over them. These have been specially condemned in England, as no matter how good the non-conducting substance--and many are so only in name--it will become rubbed off at some points, and there the bottom will be eaten both by salt water and action of copper.
Coal tar and asphaltum are the subjects of patents in various forms.
One patent claims rubber or gutta-percha dissolved in linseed oil as a vehicle in which to grind the pigment; another the same dissolved in naphtha or bisulphide of carbon as a pigment; another hard rubber, ground.
Enameling with different materials is proposed by some, while one proposes to glaze the bottoms so that barnacles and grass would find a slippery foothold.
Combinations of tallow, resin, and tar--mineral and pine--are patented mostly to use over other paints.
Coal tar, sulphur, lime, and tallow, are the subject of one patent; guano, red lead, and oil of another; while sulphur and silica are claimed by a third.
Paints containing mercury, arsenic, and even strychnine, are the subjects of several patents. A mixture of coal tar and mercurial ointment of one.
Galvanism is proposed to be used in various ways--strips of copper and zinc, or by galvanizing the plates before use. Black lead finds a place in many compositions.
One patent, by a complicated process, effects a union of metallic zinc and iron; this, granulated and ground fine, then mixed with red lead and oil, makes the paint. It is said to be the best of all the patented stuffs.
It is astonishing how many use oils derived from coal, peat, or resin, and tars of the same.