Iron minium.

Scientific American 25, 17.12.1864

Iron minium, a coloring matter founded on the iron principle, is destined to supplant red lead and other pigments that have been used until now for coating wood, iron and other metals. The advantages of iron minium are; its solidity, durability, cheapness, and above all, its property of preserving the iron completely from oxydation, and of hardening the wood. These qualities, now acknowledged by firstrate manufacturers, have assured the fullest success to the iron minium, which is advantageously employed all over Europe in the largest manufactories and sugarworks, as well as by the railway and steam navigation companies.

The great solidity of this new paint is principally due to its extreme purity. It contains no acid, no adulteration, and is therefore superior to lead minium, which contains always some sulphuric acid, a small quantity, it is true, but quite enough to attack the iron and to eat into it, after a very short space of time.

Iron minium forms a very smooth and stripeless coat upon the iron, varnishing, as it were, the metal, and preventing the atmospheric influences from having any action upon the paint.

It results, from statements made by eminent English and French chemists and engineers, that the use of red-lead and generally of all preparations in which lead is employed, is injurious to the iron coated with it. They examined vessels in which the iron, after one single voyage to the East Indies, was visibly corroded, and blisters discovered on the coating itself, containing a clear liquid, and exposing thus the iron, which presented a certain number of metallic crystals. Each blister was found to be a sort of galvanic battery, and corrosion in such a case is unavoidable, because there is always a chemical action going on, whenever electricity is produced. This phenomenon must needs continue as long as there remains any red-lead, in consequence of the immediate contact of the lead paint with the metallic surface. Red-lead, therefore, as well as any other lead pigment, ought to be completely excluded from the paint of iron vessels. The best result, therefore, has been obtained by coating with iron minium the exterior and the interior of iron vessels.

Iron minium has been tried by first-rate manufacturers, and always to their greatest satisfaction; it is employed in the most important building yards, for sugarworks, for railways and steam navigation, for the prisons of Belgium and other countries, it has been adopted by the great public services, civil and military, in almost all the countries of Europe.

Iron minium is also preferred for the under-coat of all the running railway material, the painting inside and outside of the wagons, as well as for the under and upper part of carriages. Locomotives, tenders, and iron and wooden bridges are all, with great advantage, coated by this minium. It also covers usefully all kinds of tarpaulins.

The iron minium is employed the same as all other paints, with boiled or unboiled linseed oil; if the oil is not boiled, some dryers must be added, for instance litharge or any good siccative, but not turpentine. For iron vessels or any works exposed to the contact of salt water, it is necessary to take boiled flax oil, and not to employ litharge, but a good siccative, and not to expose the object to the action of the water before the painting is perfectly dry.

Iron minium mixes easily with other colors, such as black, yellow, green, etc.; and by so doing a variety of colors is obtained, to the convenience of persons who would not like the dark brown of the iron minium paint. It has been proved by experiments that the iron minium paint lasts twice and even three times as long as red-lead paint.

Iron minium has also been employed for the painting of sugar vats, standers of iron plate or cast-iron boilers, and all kinds of steam engines; it resists generally the strongest heat. Mixed with mineral tar, it forms an excellent coat for wooden vessels, since it hardens the wood to a remarkable degree. It is most advantageous for gas tubes.

It is another important advantage of this paint, that mixed with oil there is no apparent alteration, whilst red-lead, when it remains a few days not used, shows some clots not to be reduced, and brought forward by the influence of the oil on the oxide of lead. The iron minium paint is to be applied in several layers, the first ought to be thin, the second a little thicker. The proportions of the mixtures are as follows:—One pound of iron minium to be ground with one and a half per cent of boiled or unboiled flax oil, to be added one-twentieth per cent of dryer.

— London Practical Mechanic's Journal.