Endless canvas belts have also been in favor in many white lead factories on which the heated product was dropped from the mills, carrying it a certain distance away, so as to cool down and be removed by scrapers. The drawback to this system is that unless properly looked after there is too much waste, and the risk of mixing particles of dried up skin or crust into the commercial containers. Still another method, although rather primitive, for cooling the heated lead in oil, was to have large wooden tanks of great strength holding any where from two to three tons set on the ground floor in close proximity to the mills, into which a portion of cold water had been placed and the finished lead carried to these tanks in piggins or small tubs holding about 75 pounds each and dropped into the water. When such tank was nearly filled the top of the lead was leveled off by means of trowels and more water put on if required. This was done to keep the material from forming a skin on top and was a rather handy feature, as the lead could be kept in bulk for weeks or months, thus preparing ahead for the busy season, avoiding the necessity of keeping a large quantity in small kegs and pails, enabling the packers to ship non-leaking wooden packages. Of course, since the advent of the steel packages the risk of leakage is done away with, but not the skinning or crusting over by long standing. When the lead so stored is to be filled into packages for the trade, the water is carefully taken off from the top of tank and the lead in oil scooped up with strong iron ladles into whatever sized packages are wanted. There was a time when the practice of throwing the freshly ground lead into water had to be abandoned, because it was discovered that sometimes the lead stiffened up to such an extent that it was necessary to remix and grind it over again before shipping to the trade. This happened invariably when one of the storage tanks was filled too rapidly. The remedy adopted was to first cool the lead by not placing more than one-third of its capacity of lead in any one tank twice daily, and when filled using raw linseed oil on leveling off the top in place of water. Some twenty years since a well-known firm of corroders conceived the idea of storing immense quantities of white lead in bulk, dry and in oil, and constructed a massive building of four stories with a basement. The basement was intended for the storage of commercial packages of lead in oil in wood, because this basement was of low temperature during the heated term. The first floor was for filling, packing and shipping, the second floor had a dozen large cylindrical steel tanks with funnel-shaped bottom, set in on a level extending to within four feet of the first floor, whence the lead in oil from each tank by means of a sliding gate and lever attachment could be filled by gravity into any package no matter of what size.
These storage tanks, each of which had a capacity of thirty-five short tons, and whose diameter at the top was 8 1/2 feet, were filled by means of iron trucks on wheels of a capacity of one and a quarter tons that were brought from the mills, the product already cooled and discharged by means of a sliding gate. The extra cost of this work for labor was overcome by the economy in labor in filling the commercial packages by gravity, not considering the great advantage of being ready at all times to furnish very large tonnages of the product, without overcrowding the mills. The third floor was devoted to the storage of dry white lead in bulk, of which it held at one certain time nearly 300 short tons. This may at first glance appear like an unwise accumulation of stock, but it turned out to good advantage for several reasons, chief of which was a long protracted shutdown in corrosion, the other that it confirmed what the late V. B. Grinnell, who had investigated the practical side of white lead corrosion and grinding for several years from the painters' standpoint, asserted in some of his writings, namely, that the belief that white lead in oil should be well aged was erroneous, but that the storing and ageing of dry lead was a great benefit to the quality. The writer has found that lead stored in the dry state for a month mixes and grinds more freely - ripens, as it were - and appears to be endowed with better body or hiding power. The fourth floor of the building in question was devoted to the storage of empty lead containers, and every floor had its heating arrangement by dry hot air flues.
Of course, the paint and color grinder who does not corrode his own white lead will not store very large quantities of dry lead to place on a floor or in a bin for exposure to normal atmosphere, but it will pay in the long run to purchase supplies well ahead, as even when in barrels or casks the dry lead will become more mellow and grind more freely when not too fresh, unless it be packed damp. The paint grinder who grinds paste paints consisting of part white lead and part zinc white, will do well to thoroughly examine his stock of lead for uniform dryness, because zinc white coming in contact with damp or moist white lead will give serious trouble when ground in oil in fairly stiff paste form, as lumping and partial hardness will be the inevitable result. We shall refer to this matter again when we consider the subject of grinding paste whites in general.
When grinding white lead in pale gold size or varnish for coach and car work, great care must be exercised in having the pigment as dry as is possible, and also that the vehicle is free from rosin or other soft resins.