The different qualities are separated during the process, the bole, which has the higher commercial value, being the more carefully treated. After the first separation the bole is further classed into first, second, third, and intermediate qualities--_boletta_, _fascia_, _cerchione_, &c. Its most important characteristic is termed, in commercial language, _punto di colore_, or tint. The value of the bole rises as its tint deepens. Thus bole of the third quality is lighter than that of the second, and the second than that of the first. After the third quality comes the _terra guilla_. The yellow earths, after excavation, are exposed to the open air for about a year, by the pit side, without classification. The bole, on the contrary, is placed in well-ventilated storehouses to dry for about six months. This diversity of treatment is owing to the fact that exposure to the elements brightens the colour of the yellow earths, and raises their value, while it would damage the bole by turning its darker tint first into an orange yellow, and, if continued, into an ordinary yellow earth. It also loses in compactness and crumbles up under exposure. In addition to the _punto di colore_, the size of the pieces influences the commercial value of the bole, which increases with their volume. Thus the classification is _bolo pezzo_, _bolo grapolino_, and _bolo polvere_. The yellow earths are classed as _giallo in pezzo_, _giallo commune_, and _giallo impalpabile_, the impalpable being worth more than the common yellow. The production of the Siena earths is estimated at about 600 tons per annum, of which amount about 50 tons are calcined, and the rest sold in the natural condition. The value of the trade is estimated at from £4000 to £6000. The European trade in these earths is very large. Rouen exports some 5000 tons yearly, and Havre about 1500 tons. Similar deposits occur in America, where they are known as “paint-beds,” and the earths are called “metallic paints.” A prominent example is the paint-bed at Lehigh Gap, Carbon County, Pennsylvania, which was originally opened as an ironstone mine. The mineral proved valueless metallurgically, but remarkably useful as a pigment, since it contains about 28 per cent. of hydraulic cement, which hastens the drying and causes the paint to set without any addition of artificial dryers, thereby making it eminently fitted for all outdoor application. Along the outcrop of the paint, the beds are covered by a cap or overburden of clay, and by the decomposed lower portion of the Marcellus slate, which is 50 feet thick at the Rutherford shaft. Beginning with the Marcellus slate, the measures occur in the following descending order:-- _a._ Hydraulic cement (probably Upper Helderberg), very hard and compact. _b._ Blue clay, about 6 inches thick. _c._ Paint-ore, varying from 6 inches to 6 feet in thickness. _d._ Yellow clay, 6 feet thick. _e._ Oriskany sandstone, forming the crest and southern side of the ridge.