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Book II About different applications of earths (painting, medical) and their occurrences

Book II About different applications of earths (painting, medical) and their occurrences Page of 251 Book II About different applications of earths (painting, medical) and their occurrences Text size:minus plus Restore normal size   Mail page  Print this page
22
DE NATURA FOSSILIUM
earths are found in one place, composite, in another. The presence of any of the other elements, water, air, or fire, in a simple earth can be deter­mined in the following manner. Earth is essentially heavy but one that contains air throughout its mass is light. Earth is essentially dry but when it contains any cold water it is astringent and if it contains fire it is acrid. When an earth contains both air and water it is glutinous and light while the presence of both air and fire make it light and acrid.
Simple earths are distinguished from one another by qualities and those things that are related to their place of origin. They may be meager, unctuous, or intermediate; porous, dense, or intermediate; soft, hard, or intermediate; and smooth, rough, or intermediate. They are distinguished by variations in color and may be white, black, yellow, red, purple, green, blue, gray, or brown. They differ in taste being sweet, oily, sour, oily-sweet, or oily-sour. Many earths are astringent. Some show differences in odor but this cannot be detected in most cases unless the earth is treated. The odor agrees with the taste and is usually said to be either agreeable and pleasing or disagreeable and foul. Earths differ in form of occurrence being either tabular or non-tabular. In addition, there are certain elemental differences in simple earths. They are usually dry and cool although warm or tepid earths are known and even though these are cooled they will return to their original nature. When any portion of such an earth or even the entire mass is sprinkled or soaked with water and then dried it re­turns to its former state. Some of these qualities are readily perceived by the physical senses, color by the eyes and taste by the tongue if the earth is not too disagreeable to taste. When an earth has a very disagreeable taste it is better to mix it with some sweet water and then taste the water. By touch we perceive the hardness, softness, smoothness and roughness of earths. To test the meagerness, an earth is softened with water and thoroughly worked by the hands. A small ball of this is then thrown on the ground and if it cracks open it is meager, if not, it is unctuous. Actually some earths are so unctuous that when placed on the tongue they melt like butter. Lightweight earths are porous, heavy earths, dense, while those which are intermediate in weight have an intermediate texture. The weight is determined by either holding it in one's hand or weighing it on scales. In any case it is important that the sample examined be represen­tative of the whole. I do not agree with Pliny who denies that lightness or heaviness can be determined by true weight.
Through the combining of differences various forms of earths are created. While it may not be possible to enumerate all of these as Co­lumella has done with the earths used by artisans and farmers, certainly one who discusses the nature of these things should not only classify them but also describe them very carefully.
A simple earth may be either meager, unctuous, or intermediate. An earth in any one of these classes may be either porous, dense, or inter­mediate, thus increasing the number of varieties to nine. Any of these
Book II About different applications of earths (painting, medical) and their occurrences Page of 251 Book II About different applications of earths (painting, medical) and their occurrences
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