PLASTKRINO. 



PLATE; PLATING. 



HO 



Urge quantities, or over Urge areas, although it U found in * great 

 many countries. When the carbonate* of lime are used for plastering. 

 Kiwu precautions muit b* Ukon to ensure their |>erfact hydration before 

 they are put upon the walU, as any unslaked lime will be rare to attract 

 mowture from the atmosphere, and to slake, or, ai the workmen Bay, 

 to blow." Near London the usual practice U to cover the walls with 

 a rough coat of lime so slaked, mixed with sand and with cows' hair, 

 for the purpose of counteracting the tendency of the lime and sand 

 mortar to contract unequally, and thus.to crack, in setting. This coat 

 U called the mdrrimg coal, and in good work it is left with a roughly 

 trowelled face, able to form a by for the further finishing coats ; but 

 in commoner descriptions of work, known as laid warlc, the rendering 

 coat is at once ivatnl, or worked to such a surface as to be fit to 

 receive the finishing coat. In good work upon wall*, the rendering 

 coat is then covered with a second coat, called thejfcxtfiiij one, with 

 which great pains are taken to secure its vertically and its evenness; 

 and upon this again the ttttimg coal of pure lime la applied, whieli is 

 trowelled up with more or less care according as the surface is intended 

 to receive paper or paint Upon ceilings, or wooden partitions, the 

 several rendering, floating, and setting coats are applied, in the same 

 order as above, upon laths ; and the laths themselves are either pre- 

 pared from oak or from fir. In ceilings, however, it U customary to 

 add, after the setting coat, a very fine one, composed of the sulphate 

 of lime, or of what U commonly called the " plaster of Paris," whether 

 obtained from our own or from foreign quarries. 



The manner in which plastering is executed in Paris itself may be 

 considered to present the best type of the application of the sulphate 

 of lime for that purpose. The gypsum there used is obtained from 

 the quarries of Belleville, Hontmartre, Triel, or Vaux, and it is usually 

 dehydrued in kilns heated by wood ; the stone is said to contain a 

 certain proportion of the carbonate of lime, and it certainly is harder 

 than the English gypsum, on which latter account it may be that the 

 French plastering U so much harder than the plastering executed with 

 the Derbyshire gypsum. Workmen, indeed, consider it an axiom, that 

 " the harder the atone, the harder the plaster." After the gypsum 

 has been burnt, it is ground or pounded, and applied to the walls as 

 soon as possible after that operation ; the coarser kinds are used to 

 render the uneven surfaces tolerably level, and the finishing coats are 

 executed with the finer materials. The rough rendering is often laid 

 on with a broom, and the setting coat U applied upon it by the appli- 

 cation of rather stiff plaster floated under a rule, but finished imme- 

 diately with the trowel ; in fact, ordinary French plastering is no 

 better than English laid work, and it is quite as uneven and ae 

 irregular as the latter. In the execution of their ceilings, the French 

 plasterer* adopt a different system from the one used in England ; for 

 they generally nail their laths at wide intervals, and upon them they 

 Uy slabs of old or rough plaster, which they bind together by new 

 materials, so as to produce, as it were, a single solid slab of light 

 plaster over the whole ceiling, which U subsequently made smooth on 

 the under side by the addition of a setting coat. This description of 

 ceiling U heavier than the English ones ; but it resists the transmission 

 of fire more successfully, and it is also less permeable by sound : the 

 latter inconvenience of English ceilings U sometimes obviated by the 

 introduction of sound boarding, or of pugging which, however, are 

 objectionable on the score of their tendency to develope the dry-rot in 

 the joints of the floors. 



There U one remarkable difference in the action of the lime plastering 

 and of the gypsum plastering, arising from the fact that the crystalli- 

 sation of the Utter is accompanied by an expansion so energetic, that if 

 it be not provided for very serious accidents would occur ; whereas the 

 lime plastering, as a general rule, has a tendency to contract. Of what- 

 ever materials the body of the plastering may be formed, the finer 

 moulding*, and all the cast ornaments, are executed in fine plaster, 

 unless the cements, or the prepared sulphates of lime, known as the 

 Parian, Keeoe's, or Martin's cements, are used. The class of materials 

 last named are obtained by the calcination of a previously dehydrised 

 sulphate of lime, soaked in solutions of alum, borax, Ac. ; and they 

 produce remarkably hard and smooth surfaces, admirably adapted to 

 receive paint ; unfortunately, their use is costly. 



Stucco* are made by the application, as a setting coat, of lime mixed 

 with calcareous powder, plaster, and other ingredient*, which is 

 trowelled up by dint of excessive labour to a fine surface resembling 

 marble, and able, like marble, to receive a polish. Different colours 

 are given by mixing with the lime the metallic oxides of the required 

 tints; and the poliihing is effected only when the whole of the moisture 

 has worked out of the lime. The mode of polishing is by the use of 

 fine grits, tripoli powder, and oil rubber*, in nearly thn same manner 

 as for marble. ScaglioU U in tact a species of stucco, but it is executed 

 by the Introduction of small particles of fine spars, or of coloured marble, 

 into the rendering coat, in addition to the simple lime powder, so as to 

 produce the effect of the more ornamental descriptions of marble breccias. 

 Both these ornamental kinds of work are adapted for internal deco- 

 ration, but externally they are exposed rapidly to decay. It may also 

 be added that, in the construction of concert, or even of debating- 

 rooms, it is preferable to finish the walls with ordinary plastering 

 than with stucco, or scaglioU, for the Utter materials are so elastic 

 that they reflect sound in a manner to interfere with the purity of the 

 tone. 



Whatever mode of plastering may be adopted, it is essential that the 

 walla on which it is applied should be perfectly dry, and perfectly 

 impermeable, if any elaborate surface decorations are to be applied to 

 them. Great precautions must also be taken to secure the absence of 

 organic matters in the materials used, for if any of them should be 

 present, the nitrogen salts will be thrown out, under such cireum- 

 stanoes as to destroy any painting or papering on thn walls. It is 

 precisely to the neglect of this precaution that we may attribute the 

 loss of so many noble fresco paintings. 



PLATE; PLATING. In the article JKWKU.KRY, JEWF.U IN.., it i- 

 explained that under the general name of plate are included the pro- 

 ductions in gold and silver which are stamped at Goldsmiths' Hall and 

 similar places, while jetnUrry comprises the smaller articles which are 

 not so stamped. 



Confining our attention to plate, properly so called, it may be stated 

 that all such articles made in and near London must be sent to ( ;!.! 

 smiths' Hall, after having been stamped with the maker's mark. 

 Persons used to the work scrape off a few fragments for the purposes 

 of assay; if this be found to be below the standard (in gold 18 carat* 

 fine), the article is broken up ; if of proper standard, it is stamped and 

 returned. Host of the plate is mode in and near Clerkenwell, although 

 the chief goldsmiths have their retail establishments at the West End 

 or in the city ; and there is at all times a busy system of transmission 

 between Clerkenwell and Foster Lane, where the assay office of the 

 Goldsmiths' Company is situated. The company receive fees for assaying 

 and stamping, amounting in the aggregate to about 4000/. a-year, from 

 the manufacturers. They also receive about 2'HiO/. a-year from the 

 government, for their trouble in collecting the Excise duty on gold and 

 silver plate, and paying it into the Bank of England. This curious 

 arrangement seems to have arisen from the circumstance that, as it is 

 a part of the company's duty to ascertain exactly how much precious 

 metal there is in each manufactured article, they have the means at 

 once of stating how much duty is payable to the government, at a 

 certain rate per ounce. This rate is 17'. for gold and It. 6il. for 

 if estimated at the full weight ; but as there is always a slight reduction 

 of weight during the finishing processes which follow the assaying 

 and stamping, the government take off one-sixth of the dvity, leaving 

 it at about 14*. 2c/. and Is. 3d. respectively. There have in recent 

 years been about 50,000 of these assayings made in a year. The 

 assayers are not allowed to know from whose manufactured goods the 

 particles have been scraped off ; each packet is opened, assayed, and 

 reported on with perfect fairness. If any manufacturer has erred 

 frequently by sending in goods below the standard, the officer who 

 receives the goods may direct any subsequent specimens from him 

 to be tested with additional severity. Out of London, the tow us in 

 which the largest amount of gold and silver plate is manufactured are 

 Birmingham and Sheffield ; halls or assay offices ore established there, 

 with duties nearly like those of Goldsmiths' Hall ; and at those places 

 a curious operation is conducted, relating to tlieti of gold and silver. 

 An assayer scrapes eight grains from every troy pound of plate manu- 

 factured, and divides it into two portions, one of which is at once 

 assayed ; the other is placed in a receptacle called the diet-box, which, 

 at the end of the year, contains specimens from all the articles manu- 

 factured. This box is sent up once a year to London, where the assay 

 master of the Royal Mint assays a fair average of all the small portion* 

 which it contains : if this average reaches the standard, the assayer at 

 Birmingham or Sheffield receives a certificate ; if below the standard, 

 he is fined. There ore a few other assay offices in the United King- 

 dom, each having control over the gold and silver plate made within a 

 certain district. The Goldsmiths' Company have often petitioned for 

 the abolition of these country offices, on the plea that the assays are 

 more scrupulously made by the company's sen-ants than by those of 

 the local halls ; but it is difficult to get rid of the influence of self- 

 interest in connection with any such plea. It is admitted, however, 

 that plate stamped with the London hall-mark commands a higher 

 position in the market than that which has only a country stamp. In 

 recent years there have been (in round numbers) about 10,000 ozs. of 

 gold plate, and 1,000,000 oca. of silver plate, assayed and subjected to 

 government duty annually in the United Kingdom. 



The manufacturing operations do not coll for detailed notice here. 

 The processes of rolling, casting, punching, chasing, hammering, 

 stamping, soldering, riveting, and burnishing, all come into requisition 

 in the manufacture of a piece of plate of any considerable size or elabo- 

 ration of design. 



The proportion, however, of articles of plate made of real gold or 

 silver throughout is very small compared with that of articles in which 

 the surface only is of precious metal, laid upon a metal of cheaper 

 character. By pressure between steel rollers, a thin layer of gold or 

 silver may be mode to adhere to a thicker layer of some cheaper metal, 

 and of the compound layer thus produced numerous articles may be 

 nude. A class of goods called Sheffield plate used to be very largely 

 manufactured of such compounds. The product has been consider- 

 ably improved by the adoption of a white metal for the ground or 

 foundation. This white metal is usually a compound of nickel with 

 certain other metals ; and the colour bears a. sufficiently close resem- 

 blance to that of silver to render it advantageous in all, since it will 

 not show a coppery or brassy tint when the silver is worn away. 

 Articles of real silver plate are sometimes coated with real gold on one 



