Agricola, Georgius, De re metallica, 1912/1950

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              good, for the cupels made from them, since they are not sufficiently dry,
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              frequently crack and break in the fire and absorb the metals. </s>
              <s>If ashes of
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              beech or similar wood are not to be had, the assayer makes little balls of such
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              ashes as he can get, after they have been cleared of impurities in the manner
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              before described, and puts them in a baker's or potter's oven to burn, and from
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              these the cupels are made, because the fire consumes whatever fat or damp
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              there may be. </s>
              <s>As to all kinds of ashes, the older they are the better, for it is
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              necessary that they should have the greatest possible dryness. </s>
              <s>For this
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              reason ashes obtained from burned bones, especially from the bones of the
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              heads of animals, are the most suitable for cupels, as are also those ashes
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              obtained from the horns of deer and the spines of fishes. </s>
              <s>Lastly, some take the
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              ashes which are obtained from burnt scrapings of leather, when the tanners
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              scrape the hides to clear them from hair. </s>
              <s>Some prefer to use compounds,
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              that one being recommended which has one and a half parts of ashes from the
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              bones of animals or the spines of fishes, and one part of beech ashes, and half a
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              part of ashes of burnt hide scrapings. </s>
              <s>From this mixture good cupels are
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              made, though far better ones are obtained from equal portions of ashes of
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              burnt hide scrapings, ashes of the bones of heads of sheep and calves, and
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              ashes of deer horns. </s>
              <s>But the best of all are produced from deer horns alone,
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              burnt to powder; this kind, by reason of its extreme dryness, absorbs metals
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              least of all. </s>
              <s>Assayers of our own day, however, generally make the
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              cupels from beech ashes. </s>
              <s>These ashes, after being prepared in the
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              manner just described, are first of all sprinkled with beer or water, to make
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              them stick together, and are then ground in a small mortar. </s>
              <s>They are ground
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              again after being mixed with the ashes obtained from the skulls of beasts or from
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              the spines of fishes; the more the ashes are ground the better they are.
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              </s>
              <s>Some rub bricks and sprinkle the dust so obtained, after sifting it, into the
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              beech ashes, for dust of this kind does not allow the hearth-lead to absorb
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              the gold or silver by eating away the cupels. </s>
              <s>Others, to guard against the
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              same thing, moisten the cupels with white of egg after they have been made,
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              and when they have been dried in the sun, again crush them; especially if they
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              want to assay in it an ore or copper which contains iron. </s>
              <s>Some moisten the
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              ashes again and again with cow's milk, and dry them, and grind them in a
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              small mortar, and then mould the cupels. </s>
              <s>In the works in which silver
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              is separated from copper, they make cupels from two parts of the ashes of
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              the crucible of the cupellation furnace, for these ashes are very dry, and from
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              one part of bone-ash. </s>
              <s>Cupels which have been made in these ways also
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              need to be placed in the sun or in a furnace; afterward, in whatever way
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              they have been made, they must be kept a long time in dry places, for the
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              older they are, the dryer and better they are.</s>
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              <s>Not only potters, but also the assayers themselves, make scorifiers
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              and triangular crucibles. </s>
              <s>They make them out of fatty clay, which is
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              dry
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              5
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              , and neither hard nor soft. </s>
              <s>With this clay they mix the dust of old
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              broken crucibles, or of burnt and worn bricks; then they knead with a
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              pestle the clay thus mixed with dust, and then dry it. </s>
              <s>As to these crucibles, </s>
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