After completing his account of the occult virtues of gems in their natural state, Thomas goes on to discuss the sculpture of gems and the additional virtues which they thereby acquire, a subject on which Marbod had not touched. Thomas had already announced at the beginning of his book on stones:[1296] “Moreover, at the close of this book we have given certain opinions of the ancients which we think are neither to be credited in every respect nor denied in every respect, and in this we follow the glorious Augustine. The children of Israel are said to have carved certain gems in the desert, especially carnelians, and their work of sculpture is said to have been of such subtle skill that no one since has ever dared attempt an imitation of it. And there is no doubt but that figures and images of figures are engraved according to the efficacies of the virtues of gems.” Thomas also admits that the Israelites should have been adepts in such work, when he recalls the divine direction which they received in the case of the twelve gems in the breast-plate of the high priest. “Therefore it is evident that sculptures are not found on gems without good reason. On the other hand, I would not say that every such engraving is a token of mystic virtue.” Later, when he comes to “the relations of the ancient sculptors concerning the engraving of gems,” Thomas warns that, although the form of stones is to be honored for its virtue, “yet hope is not to be put in them but, according to what is written, in God alone from whom is derived the virtue of stones and the dignity of every creature.” The astrological character of such engraved images is made manifest by the connection of many of them with the signs of the zodiac.
Thetel on images on stones.
Thomas complains that the ancient authorities for such images and their virtues are often not cited, but he had found a treatise in which the images which the children of Israel were supposed to have engraved in the desert were recorded by a Jewish philosopher named Thetel or Techel.[1297] Of this treatise Thomas makes a Latin translation for his readers, cautioning them, however, that Thetel’s opinions “are not to be trusted on every point.” Thetel’s treatise, at least as it is reproduced by Thomas who, however, has perhaps already used parts of it in his preceding discussion, begins with the sentence: “When a jasper is found and on it a man with a shield about his neck or in his hand and a serpent beneath his feet, this has virtue against all enemies.” It ends with the sentence: “When there is found on a stone a foaming horse and above a man holding a scepter in his hand, this is good for those who have power over men.” These sentences perhaps sufficiently suggest the character of the work. It is also found separately in the manuscripts as early as the twelfth century.[1298] Some of these vary considerably from the text as given by Thomas. The popularity of the treatise is also attested by the allusions in its prefaces to spurious imitations of it.
Zahel or Zaël the Israelite.
This Thetel, Techel, or Cehel, with his seals of the children of Israel, is presumably no other than Zethel or Zachel or Zahel or Zaël, the Israelite or Ismaelite,[1299] some of whose astrological treatises appeared in early printed editions,[1300] and several of whose works are listed by Albertus Magnus in the Speculum astronomiae.[1301] This Sahl ben Bisr ben Habib lived until 823 with the governor of Chorasan and then became the astrologer of El-Hasan, vizier to the Caliph al-Mamun. He was highly esteemed by the Byzantines, who called him Σέχελ or τοῦ σοφωτάτου Ἰουδαίου τοῦ Σὰχλ τοῦ υἱοῦ τοῦ Πέσρ.[1302] The translation of his works into Latin seems to have begun at an early date, as his Fatidica or Decrees of Fate was translated in 1138 by Hermann of Dalmatia,[1303] while our treatise on seals appears in a twelfth century manuscript.
Consecration of gems.
Thomas terminates his book on stones by instructions, quite in the tone of the blessed Hildegard, concerning the blessing of gems. As a result of Adam’s fall every creature was corrupted and lost some of its original virtue, and even such virtues as are left to gems are often further corrupted by the touch of impious and impure men. Hence, just as sinful men are renovated by baptism and penance, so gems can have some of their lost virtues restored by a ceremony of consecration and sanctification. They should be wrapped in linen, placed on the altar, and the priest, after saying mass and while still wearing his sacred robes, should offer this prayer:
“God, almighty Father, who showed Thy virtue to all through certain insensible creatures, who bade Thy servant Moses adorn himself among other holy vestments with twelve precious stones as a token of judgment, and also showed the Evangelist John the heavenly city of Jerusalem eternally constructed of the virtues which these same stones typify, we humbly beseech Thy Majesty to deign to consecrate and sanctify these stones by the sanctification and invocation of Thy Name, that they may be sanctified and consecrated, and may recover the efficacious virtues with which the experience of wise men proves Thee to have endowed them, so that whatever persons may wear them, may feel Thy virtue present through them and may deserve to receive the gifts of Thy grace and the protection of Thy virtue, through Jesus, Thy Son, in whom all sanctification consists, who lives with Thee, and reigns as God through infinite successions of cycles.”[1304]
The seven metals: modern plumbing.
In his book on the seven metals, namely, gold, electrum, silver, copper, lead, tin, and iron, Thomas alludes to transmutation in speaking of copper and cites a work of alchemy ascribed to Aristotle, The Light of Lights (De lumine luminum), for the assertion that the best gold is that made from a boy’s urine and brass. This statement is to be understood, however, only of the color of the gold and not of the substance. In his discussion of lead, tin, and iron Thomas cites no authorities except that once he remarks, “as the philosopher says.”[1305] Perhaps therefore we have here what is largely a contribution of his own. At any rate it seems to include the first mention of the invention of modern plumbing.[1306] Tin, Thomas tells us, rusts out easily if it lies long in water. Therefore the underground pipes of aqueducts have long been made of lead, but they used to be joined with tin, but in “modern times” human art has thought out a method of uniting them with hot molten lead. For while tin will not remain solid for long, “lead lasts forever underground.” Thomas goes on to say that lead has the peculiar property among the metals of always increasing in size. Like Hildegard, he also mentions steel, which he says is hardened by many tensions so that it surpasses iron in virtue. He further tells of an oriental iron[1307] which is very good for cutting and is fusible like copper or silver but not ductile like the iron in other parts of the world.