Yellow Ocher is first and foremost among the yellow pigments because of the great quantities consumed, both in the dry state and ground in oil. Years ago it was thought to be indispensable as a priming or first coater for raw wood on exposed surfaces, such as the frame dwellings and buildings going up all over this country by hundreds of thousands. The experience of many years has brought about a revulsion in the ocher priming practice, and this has been caused by the gradual enlightenment of consumers that it is a fallacy to assume that anything in the paint line is good enough for the priming coat. While that idea was prevalent among the trade, disreputable painters and ignorant consumers were in quest of cheap priming ochers, and many grinders made it a practice to cater to such trade in order to reap a harvest while the sun was shining, and outbid competitors. In order to produce a so-called yellow ocher in paste form at low cost, some ground up French yellow ocher with two or three times its own weight of barytes, thus saving in the cost of linseed oil, and these were not the worst specimens on the market, while others went further in the sophistication principle by mixing the cheapest kinds of domestic ochers with still cheaper whiting, off-colored barytes, marble dust or clay, and grinding such mixtures in part linseed oil and part mineral oil, giving the material a bright effect by the addition of a trifle of chrome yellow, and such dopes are still made and sold to-day, although the grinder will not at all times place his name upon the package. It stands to reason that material of that description cannot make a foundation for the paint to be applied over it as a finish, and that is one of the chief reasons why priming with ocher has shown itself to be a disastrous failure, on account of its inevitable scaling clean to the wood, if not after the original painting, then surely after the repainting. On such timber as Southern pine, cypress, sycamore, birch or maple, even the best French yellow ocher, ground in and thinned for the purpose with pure raw linseed oil, is unsuitable, unless it is mixed with at least three times its weight of lead carbonate (corroded white lead), while for such lumber as whitewood, white pine, spruce and hemlock, etc., a priming made from finely ground French ocher in sufficient raw linseed oil, used rather thin and well rubbed in, will not be apt to split and throw off the top coatings of paint. Of all yellow ochers, that imported from France is preferred, and the United States Navy Department specifications call for a yellow ocher to equal the best French ocher in color, shade, tone and strength, containing not less than 20 per cent sesquioxide of iron, not over 5 per cent of lime in any form, balance to be of the natural gangue that occurs with it in nature, which means silica and aluminum silicates. It will not be uninteresting to note that in France the mining, levigation, drying, etc., of ocher is much more primitive than elsewhere in the world, and yet the cost is comparatively low because of the great area available for the purpose. In England, Germany, Italy and the United States the mined ocher earth must be put through a more or less costly process of milling in the wet, floating, drying in kilns or chambers, sifting, powdering and sorting, while in France the mined earth is spread over an area varying from 3,000 to 6,000 square yards, through which ditches are dug that lead to basins which are arranged over one another. During the summer months all work is stopped. In the fall of the year, during the rainy season, the water runs through the ditches and carries the earth slowly to the next basin. Here the coarser particles sink to the bottom, while the finer portion is floated to the next basin, and so on until all the earth has been well levigated. Throughout the winter, while there is no freezing, this natural floating apparatus does its work, until the whole area is free of the ocher earth and the basins full of it. A few weeks later the basins are drained as much as possible of clear water, and the sun of early spring finishes the evaporation of the remainder. When the yellow earth has dried up so far as to show large furrows it is taken up and spread on trays in thin layers and dried by the heat of the sun, and, this accomplished, it is filled in casks and made ready for the market. The fineness of the floated material makes pulverizing in a mill or sifting apparatus unnecessary. In the marking of the packages the French ocher producers are really practical. Each cask bears a general designation, denoting the quality, as, for instance: Qualite extra superieur (extra fine quality), qualite superieur (fine quality), Ire qualite (good or prime quality). In addition to these general designations will be found on each package such letters as J. L. C. E. S., J. F. L. E. S., J. T. C. E. S., J. O. L. S., and so on. J. stands for jaune or yellow, L. for lave or levigated, C. for citron or light yellow, T. means tres or very, E. for extra, F. for fonce or dark, O. for or (or gold), R. for rouge (or red), M. for mijico, a very desirable shade, so that these letters give an idea of the sort of ocher contained in the casks, which usually run between 340 and 360 kilos gross weight. Some importers have the French producers mark the casks with such marks as citron, satin, or with the initials of their firm names. These ochers of the pale shade show anywhere from 17 to 22 per cent sesquioxide of iron, but there is at least one brand of J. F. L. E. S. (dark shade) that analyzes from 26 to 28 per cent in sesquioxide, and this is usually selected for grinding a brand known as Oxford ocher in oil. Having thus described the trade marks of French yellow ocher, we would say that the color grinder will have no difficulty in selecting his needs by testing the samples offered for shade, tone, fineness and strength in the usual way, making rub-outs or trial grindings. When once a certain brand has been adopted, there is no trouble in obtaining the same quality right along, for as a rule the exporters as well as the importers see to it that the standard is well kept up to the mark. There is not enough margin of profit for either to take any great risks. The precaution necessary in the mixing and grinding of French and other yellow ochers is to see that the material is as dry as possible; in other words, bone dry. Oftentimes it so happens that a cargo in crossing the Atlantic Ocean will become more or less saturated, and the moisture will not evaporate while enclosed in the cask, therefore the ocher should be spread on drying pans or other apparatus suitable to the purpose, because moist or damp earth paints will not mix with the minimum quantity of oil and pass through the mills in lumpy condition, even when an excess of oil is used. At least a good, smooth paste cannot be produced with damp material. For grinding ocher in paste form, any good stone mill of a diameter between 24 and 30 inches, with not too high a speed, will render good service, and for French ocher of good fineness the soft or esopus stones are preferable, while for the more gritty English, Italian and domestic ochers buhr millstones are better suited. French yellow ocher for the general trade, ground pure in paste form, is best mixed 72 pounds pigment and 28 pounds raw linseed oil, and boiled linseed oil should not be used, as it makes the paste too soft, and on standing about in containers the oil is apt to separate. When grinding large batches of ocher in oil into one package, the material in the middle of such package is often found to form hard lumps. This is due to overheating in the mill, or it may be due to moisture in the pigment or in the oil, but can be avoided by using smaller containers, in which the paste may cool more rapidly and then be dumped into the larger package, or by having the paste run from the mill into a mixing can with stirring device.
The color in oil sold by reputable manufacturers as French ocher or French yellow is that which is ground from the J. L. C. E. S. or citron brand, while the satin brand is also favored to some extent. Special brands of Yellow Ocher in Oil, when pure, i. e., without any extending material, are either made from the best grades of Pennsylvania mines, which are not so high in iron oxide, but of fairly good color, some of them approaching second or third grade French ochers in point of color and requiring about 75 per cent of pigment to 25 per cent of oil by weight to form a good paste. When, however, prices of the dry ochers are compared and percentage of oil required is considered, it will be found that the small difference in cost does not warrant the color grinder to place such a brand on his list as yellow ocher without the prefix "French," because he cannot obtain a high enough price. The Southern ochers, mined in Virginia, Georgia and Alabama, are usually very high in oxide of iron, some running as high as 64 and even 72 per cent, but their color is exceedingly dull, and the demand for them is limited to the use in backing up floor oilcloth and as an oxide of iron filler in certain specification paints for railroads, and also to furnish the necessary oxide of iron feature in doped brands of ocher.