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PROTEAN STONE, OR ARTIFICIAL IVORY—CLACKING.
[Class XXIX.
tallow candle. (See the Prefatory Notice respecting therecommendation for the award of the Council Medal.)
Quanonne, C. and L, Cureghem, Brabant (Belgium ,431, p. 1335). Prize Medal. The manufactory of theseexhibitors, which was the first established in Belgium , isone of the offshoots of that of De Milly, in Paris ;hence they adopt the name for their candles which wasgiven to stearic candles by their instructor, namely,“ Bougies de /’ Etoile” As regards colour and hardness,their stearic acid leaves nothing to desire; but their can-dles are not quite so carefully moulded as they might be,and have not that high degree of polish which is expectedin candles of first-class manufacture in other respects.
Rossi and Schiapparelt, Turin (Sardinia , G, p. 1302).Honourable Mention. Though the Jury did not find thestearic manufactures of these exhibitors quite equal tothe best examples, they consider the stearic acid andcandles to be carefully made, and therefore accord theman Honourable Mention.
Saixte and Co., Cossypore (India , p. 922). Honour-able Mention. The Jury have much satisfaction in makingan Honourable Mention of the very good stearic candlesmanufactured in India by Messrs. Sainte and Co. Thelocal manufacture of stearic candles deserves every en-couragement, as they are peculiarly suitable to hot cli-mates, on account of their high fusing-point, and as theremust be a large quantity of fats of little value, whichwould answer well for their production.
Sapelktk, V., Moscow (Russia , 309, p. 137G). Ho-nourable Mention. The Jury accord to M. Sapelkin anHonourable Mention, in consideration of the great carebestowed on the manufacture of wax-candles for church-service ; many of these are tastefully ornamented with asimple spiral of gold, and have a very elegant appearance.The equality in size of the candles, as compared with oneanother, and likewise of their diameter throughout theirwhole length, are points deserving commendation. Itappears that in the Greek Catholic Churches only waxor vegetable oil is allowed to be burned.
ITT. PROTEAX STOXE, OR ARTIFICIAL IVORY.
Under this title there are exhibited, in Class XXIX., anumber of articles, such as door-handles, finger-plates,inkstands, and letter-weights. These very beautiful objectsare composed of a new material, derived from gypsum(native bi-hydrated sulphate of lime), which, by numerousvariations in the method of treating it, is made to re-semble ivory, granite, and various kinds of marble. Fromthe specimens exhibited it appears to be very hard, andcapable of taking the highest polish, which, it is said, isperpetuated by uso. It is translucent and brilliant incolour, and, being tinted throughout the mass, the mar-bling and mottling are not liable to be rubbed off. Itappears to be applicable to many purposes for which ivoryand marble are at present used; but it is not fitted to bemade into knife-handles, on account of its brittleness.
In order to illustrate this very ingenious manufacture,we must rccal to the recollection of the reader the veryfamiliar phenomenon of the solidification of a mixtureof plaster-of-Paris (de-hydrated sulphate of lime) andwater, which arises from the circumstance that the anhy-drous sulphate of lime recombines with water equivalentin quantity to that of which gypsum is deprived by heatin the formation of plaster: but, as under the conditionsof this solidification the plaster is diluted with far morewater than it can recombine with, it results that a portionmust be left in a free state in the interstices of the mass,which is consequently opaque, and, on drying, becomesporous; and although it is the same in chemical composi-tion, it differs greatly in its physical aspect and propertiesfrom the native compound gypsum or alabaster, which iscrystalline and translucent.
In reflecting on the cause of this difference, it occurredto Mr. Cheverton that if the combination of water andanhydrous sulphate of lime could be slowly effected,whilst the latter was in a state of compression, an arti-ficial stone might be produced, compact and crystalline intexture, and translucent in appearance. This view wasfully confirmed by a series of experiments.
The process by which these results are obtained is de-scribed in the specification of Mr. Cheverton’s patent,obtained in June 1S50, as consisting in the de-hydrationand subsequent re-hydration of native bi-hydrated sulphateof lime, either in a compact form, as alabaster, or in thestate of a fine powder. In the first instance the alabasteris wrought into the required form; and in the second, thematerial, in the state of a very fine powder, is compressedinto a mould of the proper shape.
In either case, after the object has been fashioned, it isexposed for 48 hours to a temperature of from 121° to177 ^ C. (250 3 to 350° F.), by which means the wateroriginally combined with the sulphate of lime is drivenoff. The substance thus becomes very friable, but stillretains the form into which it has been wrought. Some-times plaster-of-Paris itself is compressed into moulds,but the article so formed is still subjected to the operationjust described, notwithstanding the previous baking ofthe gypsum.
If a translucent appearance is required to be given tothe surface of the figure, it is, before re-hydration, im-mersed into “ white hard varnish,” olive-oil, or other“ oleaginous matter,” until the surface is saturated; butif an opaque surface is desired, then this operation isomitted.
To effect the hardening, the object is plunged for aninstant only into water heated to a temperature of from38° to G5-J' C. (100° to 150° F.). This operation is re-peated at intervals of from 10 to 15 minutes, until thesulphate of lime is completely saturated. The mass thenbecomes crystalline and much harder than alabaster ; acircumstance which induces a belief that the new sub-stance contains a quantity of water in combination dif-ferent from that in the native body: or, in other words,that it is a new hydrate of sulphate of lime. The successof this part of the process depends in a great measure onthe very gradual manner in which the combination withwater is managed ; for without due care the material de-crepitates, and the article is then destroyed.
The colouring is effected by dissolving the requisitecolours in water, and either sprinkling the object hereand there with the coloured solution, so as to produce amottled appearance, or else by immersing it altogether inthe dye, which produces an uniform stain. This opera-tion is performed previous to that of dipping in oil orvarnish.
To the only exhibitors of this branch of manufacture,
D. Staicht and Soxs (252, p. 802), a Prize Medal isawarded.
IV. BLACKING.
Although the compound which we now call blacking(French , ^Cirage) is, in all probability, of very recentinvention, nevertheless it appears to have been customaryto imbue shoes with an oily mixture before the time ofPliny , since it is stated by him that Cato recommendedthe dregs of the olive (after the expression of the oil) tobe used for anointing bridle-reins, leather-thongs, andshoes, in order to render them supple.* It must, how-ever, be remarked, that a mixture somewhat similar tomodem blacking is also described by the same author,tand it appears quite natural to infer the occasional use ofit for renovating the black colour which we are also in-formed was given by shoemakers to leather, by means ofvitriol :% two kinds" of substances of this name beingknown, namely, blue-vitriol (sulphate of copper) andgreen-vitriol (copperas, or sulphate of iron).
The mixture alluded to was chiefly used for ink, whenceit was commonly called atramentum. It was composed oflamp-black, gum, and vinegar, and would, therefore, onlyhave required the addition of oil and honey to make itinto a tolerable blacking. This inference is rendered themore probable from the discovery of the remains ofleather found in the Roman gravel-pit discovered indigging the foundation for the New Royal Exchange,which appears to have been covered with a sort of black-