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conjectures about their materials for colouring! this feems the molt probable fubftance ; and there is a way of preparing a colour from this, much iuperior to that now in ufc, which we call fmalt.
Cobalt is a mineral containing arfenic and a blue verifiable earth. The common way of preparing fmalt is, by roafting this cobalt in a reverberatory fire. This difpofes it to vitrify, and drives off the arfenic it contains in fumes, which collect- ing at the top, form true flowers of arfenic. It is very cer- tain, however, from experiments, that if this arfenic could be preferved in the cobalt, the fmalt would be of a much finer colour ; for there are fome kinds of cobalt which yield fmalt without previous roafting; and as the arfenic is in a great meafure contained in thefe, the final ts are much finer coloured. Arfenic added to fmalt, while in fufion, greatly exalts its co- lour alfo ; and there is a way of procuring fmalt from cobalt without fire, only by diflblving it in an acid, and precipitat- ing that fo'ution with oil of tartar. The fmalt thus precipi- tated to the bottom, is of a much finer colour than any pre- pared by fire; but it is much moreexpenfive, and prepared in lefs quantity. It is very poflible, that the Chinefe might have
■ the art of making this kind of fmalt before they knew us, and that to this was owing the fine blue of their porcelain ware : but when we trafficked with them, and they purchafed fmalt fo much cheaper of us than they could make it them- felves. they naturally difcontinued the manufacture of their own finer kind, without confidering how greatly inferior the colour was which the other yielded. If this be the cafe, it will be eafy to revive this art, and the adding the true old china blue to our European manufactures, in imitation of porcelain, may give them a value which they have not at prcfent.
The Chinefe had once a method of painting the figures of fifhes and other things on the infides cf their vefTels, in fuch a manner that they did not appear til] the veflel was filled with water, or fome other clear liquor. They called this fort of china-ware kiatjttn, that is to fay, the concealed blue china. The art is now in a great meafure loft; but there may be fome guefs made as to the manner in which it might be done at this time. The vefTels which are to be made m this man- ner, nui ft be very thin : the colour muft be laid on in form of the fifh or other animals or figures, on the infi.de, after the veflel has been once baked. After this colour has had time to dry, the infide of the veflel muft have a fecond coat of the fame earth, or (tone-ware, of which the veflel is made ; and over this a varnifh of the common kind. The confequence of this will be, that the figures of the fifh, in a very ftrong colour, will be buried between two coats of the ware, which together form a compleat veflel. The outfide is then to be ground down almoft to the figures, and when they begin to appear, a new coat of the varnifh muft be laid over this. The figures will then be obfeure, and fcarce, if at all per- ceivable ; but on filling the veflel with water, the tranfparence of the fides will be taken off, and the liquor will make a fort of foil behind, which will throw out the figures of the fifh. This might be done in any ware tolerably clear and tranfpa- fent. The porcelain of China would fucceed beft with it;
' but the pains and nicety required are too great, and all the attempts lately made by them have mifcarried. See the article Staining of porcelain.
" The Chinefe make a great variety of figures on the furfaces of the vafes of white china-ware, and there is one kind of this greatly in efteem among them, in which there are flowers and other figures ; yet the fur face is quite fmooth, and the fub- ftance extremely thin. The manner of making it is this: they firft form the veflel of the fineft materials, as thin as they can ; then, when they have polifhed it infide and out at the wheel, they put into it a ftamp of its own fhape, but cut with all thefe figures : they prefs this down fo firmly on the vet moift veflel, that the impreflion is received in a very per- fect manner; and if the fhape of the veflel be at all hurt, they take it to the wheel again to reftore it. They then finifh
" it with the knife and feiflars ; and when they have made it as perfect: as can be, they cover it with the fine white varnifh within and without. This fills up all the cavities of the im preffion, and gives a perfectly fmooth and even furface; yet the thicknefs of this varnifh in the traces of the figures gives it a different white, and the whole figures are as finely and ac- curately feen, as if painted on the outfide. This is an arti- fice that might eafily be brought to bear among us, and feve- ral of our finer wares would make a pretty figure with it. 'There is a current opinion among the Chinefe themfclves, that the porcelain-ware of former times was greatly fuperior to that which they make at prefent ; and that the burying china in the earth for a long time, adds to its beauty ; but all this is founded on error. The truth is, that our merchants beat down the price of the ware, and thereby compel them to make a worfe kind in general; but they are able to do as fine things now as ever. What gave birth to the opinion, that burying porcelain-ware made it good, was, that finer pieces than ordinary are fomettmes found buried.- Thefe are all pre- cious vafes, which the poileflors buried by way- of fecurity in the times of civil war; and it is no wonder, that there are Suppl. Vox; II.
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none but of the fined kind found buried on thefe occaficlH. Ubierv. lur les Coutum. de I'Afie.
PORCELLANA, in natural hiftory, the porcelain-Jhell, or concha venerea, the name of a genus of [hell -fifh, the charaAers of which are thefe : they are of the univalve kind, and have for their mouth a long and narrow flit, dentated on eacii fide, and are of a conglobated, oblong, gibbofe, or umbonated form. This genus of (hells originally had the name perceUana and concha venerea from the refemblance of its mouth to the puden- dum muhehre, called by fome of the Roman writers, porculus and porcellus, and always alluded to under the word Venus. We have ot late fo far mifimderftoed the name as to fuppofe it derived of the word porcelain, from an imagination, that the Chinefe porcelain-ware was made of it. Gefner has fallen into the opinion, and Aldrovand Teems to have been miftaken in regard to its other name, concha venerea, fuppohV it fo called becaufe of its beauty, and therefore facred to Venus. Rondeletius calls it the remora Mutiemi ; and the murex of the fame author. Aldrovand de Teft. L. ?. p 3C2 Gefner Rondelet. de Teft. L. 2. p. 101. '
The name concha venerea may be apt to create confufion, be- caufe there is another file!] of a very different kind, a bivalve, called concha veneris. This genus is therefore much better diftinguiftied by the name porcellana. There is a prodioious difference among the fpecies of this genus ; fome are heavy, others very light ; fome have the mouth placed in a longitu- dinal, others in a tranfverfe direflion. The gibbous porcelain is a very remarkable fpecies, as is alfo the egg-porcelain, which has two buttons at the extremities ; and the egg-porcelain call- ed the navel is not lefs remarkable than thefe; this has, inftead of a button, a long beak at each end.
The mouth of the porcelain muft be narrow and oblong- this is the great charafleriftic, and is ufually dentated either on both fides or on one.
The fpecies of porcelain are fo numerous, that it may be pro- per, in the enumeration of them, to arrange them under fome regular heads. See Tab. of Shells, N°. 1 6. Some porcelaines are conglobated, and thick ; of thefe the cabi- nets of the curious afford us the following fpecies : i. The msp-porcelain, fo called from its lineations, refembling the (Sokes of a map. 2. The lettered or Arabian porcelain ■ this is fuppofed in its lineations to bear fome refemblance to Arabic charaflers. 3. The tyger's (kin porcelain. 4. The ferpent's (km porcelain. 5. The fea-loufe porcelain. 6. The millepede porcelain, 7. The punctuated porcelain. 8. The grey porcelain. 9. The Chinefe Iraki's. 10. The porcelain whofe end terminates in a fpire ; or the Violet p'&celafB-. this is but the former fpecies with its outer coat taken off. ' The reddifh porcelain. 1 2. The variegated porcelain. The tortoifc-fliell porcelain. 1 4. The guttated porcelain. The porcelain with its middle divided into four zones. The blue oval porcelain. Some porcelains are thin, and of a pyriform figure. Of thefe we have the following : 1. The pear-porcelain, with an arch- ed mouth, and variegated with yellow fpots. 2. The pear- porcelain, with an arcuated mouth and two zones. 3. The egg-porcelain, with numbers of fmall protuberances, or obtufe umbos : this is called by fome writers ovum Rumphii, or Rum- phius's egg. 4. The cloth-web porcelain. 5. The oblono- and .thick porcelain; 6. The great Argus porcelain, fo called from its being variegated with round fpots, refembling eyes. 7. The leffer Argus porcelain. 8. The pfeudo-argus, or baf- tard-eye porcelain. 9. The leveret porcelain. 1 o. The green- ifh itraU-pox porcelain, it. Thewhtiith porcelain, with rough protuberances. 1 2. The rri\\\e<peie porcelain. 13. Themoufe porcelain. 14. The mole->W«'». 15. The yellow porce- lain, with four red zones. 16. The brown porcelain, with four yellow zones 17. The Panama porcelain, with ama- thyftine circular ftreaks. )8. The green fpotted porcelain. 19. The virgated agate porcelain. 20. The blue porcelain. 2 1 . The blue fpotted porcelain.
Some of the porcelains are gibbous. Of thefe we have the fol- lowing fpecies : I. The milky porcelain, with rofe-coloured protuberances and a dentated lip. 2. The white gibbofe por- celain, with a fmooth lip and no tubercles. 3. The yellow porcelain, with a fmooth lip and no tubercles. 4. The por- celain called Congo matey and Guinea money : this has a den- tated mouth, and has fix protuberances on the back. 5. The great gibbous porcelain. Hid. Nat Eclairc. p. 308.
PORCELLIONES, in the materia medica, a name given by fome to the millepedes.
PORCELLO, in the glafs trade, the inftrument with which the workman, after having made the opening for the bowl of a drinking glafs or other fuch veffe!, with his pafiage, widens and renders it more capacious at pleafure. Neri's Art of Glafs, p 247.
PORCELLUS Cajfovienjls, in medicine, the name of a difeafe to which the people of Hungary and Poland are very fubjefl-. It is a hard tumour of the belly, attended with wind and vio- lent pains. It is truly an infaraion of the fpleen, and is to be cured by aperitives. Phil. Tranf. N°. 243. See Spleen.
Force i.i.us hdicifs, in zoology, a name given by authors to the animal called with us the Guinea pig.
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