A natural history of fossils / By Emanuel Mendes da Costa ... Vol. I, pt. I.

  • Emanuel Mendes da Costa
Date:
1757
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Licence: Public Domain Mark

Credit: A natural history of fossils / By Emanuel Mendes da Costa ... Vol. I, pt. I. Source: Wellcome Collection.

    300/316 page 284
    This is the general appearance of the true antient or Egyptian porphyry; but the porphyry nodules, found loofe on the fhores, &c. of Europe, flightly differ in the ground colour, which is generally of a fine deep brown, with a purplifh caft, fometimes only of adull brown, without any tinge of purple, and the {pots are large, thinner fet, and not quite fo angular. This ftone is very heavy, and is of fuch extreme great hardnefs, that it exceeds in this quality all the other ftones of ftrata known to me, and equals the ja/pers and many other nodules of a cryftalline bafis, that can be workt only by emery, &c. in the lapidary way, and which intirely refift inftruments of fteel, or the mafon’s work, : | This exceffive hardnefs of the porphyry, and ophites antiquorum (likewile a {pe- cies of porphyry hereafter to be defcribed) and their refitting being work’d on by inftruments of fteel, or mafon’s tools, has planned a fubject of debate among the Jearned, how the antients work’d the porphyry into the ftatues, columns, va- as the moderns find the utmoft difficulty in cutting thefe ftones. Many have, for that reafon, imagined, that the antients had fome method of hardning their tools, now unknown. Dr. Lifter, who favours this opinion (1) fays, that there - is certainly fomething loft in this age, as to the manner of fteeling of tools to work or grave on porphyry, and many, to retrieve this loft art, have, on what principle 1 own myfelf ignorant of, imagined a method (2) of hardening of tools to make them proper to cut porphyry, by fteeping them in the juice of the plant called dears breech, ox brank-urfine (3). For my part, I doubt much if the antients were acquainted with any method of tempering their ftee], in a fuperior degree to what we now do; I am apt to believe their continued affiduity and unwearied patience were the tools with which they performed their arduous work, joined to an accurate knowledge of the other materials, anfwerable to the nature of the ftones they workt on. I therefore give it as my opinion, that the temper the antients gave their ftee], did not exceed ours; I fhall further add, that I even believe it impoffible. to give fteel fuch atemper as to work freely in the mafons or flatuaries way on porphyries, ja/pers, or fuch like exceeding hard ftones. Before I proceed to give my conjecture, inwhat manner the antients work’d on this ftone, it is neceffary to inform my readers, that thefe works of porphyry are of the moft early ages of the world, and_of many. centuries before the Gre- cian or Roman era; for all the columns, ftatues, vafes, &c. now known, are of Egyptian workmanfhip, nor does there appear any either Grecian or Roman works made of it; in like manner the granite was workt by the Egyptians; thefe were ftones natural to their country, and indeed for that reafon only, we have ftill remains of Grecian workmanfhip of the fpecies of gramite, defcribed Ne. 3. fupra, in the Archipelago iflands and Afia Minor, for,thofe countries abound with that ftone; it even appears, that the porphyry was not greatly (1) Phil. Tranf. N°. 203. The true Royal Society, Vol. I. p.238. Vol. II. way of making of fteel, by Dr. Mar- p. 73. et alibi paffim, ; tin Lifter. Lowthorp’s abridg. Vol. IE. (3) dcanthus fativus, Carduus acan- «500. thus five branca urfina botanicorum. (2) Vide Birch’s hiftory of the , efteemed
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