=Basic Carbonate-White Lead.= This pigment is made by stacking clay pots containing dilute acetic acid and lead buckles, in tiers, and covering them with tan bark. Fermentation of the tan bark, with subsequent formation of carbon dioxide acting on the acetate of lead formed within the pots, produces basic carbonate of lead. After complete corrosion, the white lead is ground, floated, and dried. Corroded white lead has a specific gravity of 6.8 and contains about 85% lead oxide and 15% of carbon dioxide and water. Its opaque nature and excellent body renders it extremely valuable as a constituent of paints. Checking and chalking progress rapidly when the pigment is used alone. The various sized particles, both large and small, resulting from the corrosion process, are prominently shown in the photomicrograph. [Illustration: Crystals of Cerussite in Old Dutch Process White Lead. (Greatly magnified)] [Illustration: White Lead (Quick Process)] On account of its alkaline nature, this pigment acts upon the saponifiable oil in which it is ground, forming lead soaps which accelerate chalking of white lead--the greatest evil attending its use. Solubility in carbonic acid of the atmosphere and decay in the presence of sodium chloride may be active causes of the rapid chalking of this pigment at the seashore. Checking in some climates appears to proceed rapidly on white lead paints, in a deep hexagonal form, leaving a series of rough crests and cracks. This checking is secondary to the chalking which takes place. [Illustration: Corrosion cylinders used for making Quick Process White Lead] [Illustration: Lead Melting Pots] =White Lead (Quick Process).= By acting on atomized metallic lead, contained within large revolving wooden cylinders, with dilute acetic acid and carbon dioxide, the quick-process white lead is produced. Its value is equal to the Dutch-process white lead, and it is considered by some as possessing greater spreading value. [Illustration: Sheet iron box luted at bottom with water. Atomized lead, blown into box with steam, falls to bottom and becomes hydrated (Mild Process)] [Illustration: _Photographs courtesy of Stowe Neal_ View of agitation tanks for making Mild Process Lead] [Illustration: Steam Jected Pans for Drying White Lead]