P L A

310

P L A

a cement that is impervious to water, and may be success-fully employed in ice-houses, cisterns, tanks, &c. (SeeCement, and Mortar.) In his specification, Mr. Parkerobserves, “ nodules of clay, or argillaceous stone, generallycontain water in their centre, surrounded by calcareouscrystals, and having veins of calcareous matter. They areformed in clay, and are of a brown colour, like the clay.”These nodules, he directs, should be burned, after beingbroken into small pieces, in a kiln, with a heat nearly sufficientto vitrify them ; after which they are to be reduced to pow-der. Two measures of water added to five of this powder,produces tarras; lime and other matters may be added orwithheld at pleasure: and the proportion of water maybe varied. The term of the patent having expired, there aremany other manufactures of this cement, which are foundto be of equal goodness as to quality, and some of them ofrather a better colour than the original; a recommendation,or rather improvement, of considerable importance, since thefresco-painting, or whitewash, laid upon Mr. Parker’s com-position, when applied to the fronts of houses, is soon takenoff by the rains, and leaves the walls of a dingy and unplea-sant appearance.

An allusion has been made above, to the fresco-painting,or staining, laid upon walls plastered with this cement : thisis done to give them an appearance of stone-buildings, andis performed by diluting sulphuric acid (oil of vitriol) withwater, and adding the fluid ochres, &c., to give the requiredtint. When the stucco is washed over with this kind ofpaint, the affinity existing in the iron of the cement ceases,the acid and colour suspended in and upon the stucco is fixed,and the surface assumes, when dexterously. managed, theappearance of an ashlar bond of masonry.

Columns, &c.,done in' Scagliola , is a distinct branch ofplastering, discovered or invented in Italy , where it has beenmuch used, and thence: Introduced into Prance, where,having fascinated all the cognoscenti, it obtained the title ofscagliola. The late Henry Holland, who first brought it toEngland, engaged the artists from Paris to execute it; someof whom, finding a demand here for their labour, remainedin the country, and instructed our own workmen in the art.Columns and pilasters are executed in this branch of plas-tering, in the following manner. A wooden cradle, composedof thin strips of deal, or other wood, is made to represent thecolumn designed, but about 2^ inches less in diameter thanthe shaft is intended to be when finished. This cradle islathed round, as for common plastering, and then coveredwith a pricking-up coat of lime and hair : when this is quitedry, the artists in scagliola commence their operations, and,by an imitation of the most rare and precious marbles, pro-duce a most astonishing and delusive effect; for, nothingshort of actual fracture can discover the counterfeit: and anystone, partaking of tlje quality of marble, may be exactlyimitated by it; the imitation taking as high a polish, andfeeling to the touch as cold and solid, as the most com-pact and solid marble. The workmen select the purestgypsum they can obtain, which, after breaking it into smallpieces, they calcine. As soon as the largest fragments losetheir brilliancy, the fire is withdrawn ; the calcined powderis passed through a very fine sieve, and mixed up as it is tobe used with a solution of Flanders glue, isinglass, &c. Inthis solution the colours required in the marble to be imitatedare also diffused : but when the work is to be of variouscolours, each colour is separately prepared, and they areafterwards mingled and combined, nearly in the same man-ner that a painter mixes the primitive colours on his palette,to compose his different tints. When the powdered gypsumis prepared and mingled for the work, it is laid on the shaft

of the column, &c. 5 over the pricked-up coat of lime a® jpeand then it is floated with moulds of wood, mad e (foerequisite size, the artist using the colours necessary 1 n ,eimitation during the floating, by which means they y t \ t emingled and incorporated with the surface. To g'^j,.edwork the requisite polish, or glossy lustre, so much a j C e"in works of marble, the workman rubs it with a P.^ fl ,jtlistone with one hand, while with the other he cleans oi ],a wet sponge. He then polishes it with tripoli andc 1 g 0 fand fine soft linen ; and after going over it with a Pfelt dipped in a mixture of oil and tripoli, he fi nlSprocess by the application of pure oil. ^ co n '

This imitation is the most complete that could ^ re alceived ; and, when the bases and capitals are made ^ g y 0 ndmarble, as is the common practice, the deception isdiscovery. When not exposed to the weather, it is itsinferior to real marble in point of durability) re gng e 0lustre full as long, and is not one-eighth of the expthe cheapest imported. e by *

There is another species of plastering, though (1 ^ a[J1 g o‘distinct set of persons, known to the public by the ^ a rtscomposition ornament, used not only for the decoratn^jng'of architecture, but also for the frames of pictures, >v lieHglasses, &c. This composition, which is very str° 8 r0 pot'quite dry, and of a brownish colour, consists of 41 gj u etion A _ J - -p_i i -- 1 ."*? ■**

of two pounds of powdered whiting, one P° ul l to getl* erin solution, and half a pound of linseed-oil, mixe ^ \vl )0 ^in a copper, heated, and stirred with a spatula till j g 9 udis incorporated. After being suffered to stand to ^ting’cool, it is laid upon a stone, covered with powdere a perand beaten till it assumes a tough and firm consiste ^ o( j lg towhich it is put by for use, and covered with. "' ekeep it fresh. The ornaments to be cast in this aft**'are modelled in clay, as for common plastering, hoX .vvo ^

he

uic muueiieu in oicty, as tor euniiuoii piaj joS*™wards a cameo, or mould, is carved in a block ot ne# tnThis carving requires to be done with the utro

ornament - m

and truth, otherwise the symmetry of the j 9 ■ »

cast from it will be spoiled. When the comp oS1 s \ze 0used, it is cut with a knife into pieces adapted t0 ^ fer y p 9 ’’'the mould, and forced with the hand closely m t0 sC reV' r >, 'It is then placed in a press worked by an * 10n a fter be’ 11 ”which it is farther compressed into every crevice • . ( j e .(3o" ,I,,

removed from the press, the mould is turned u J gn jposit' <, !j|with a smart tap on a board, which dislodges the c ^ e foot ^and the mould leaves it with its face upwards. ^ a|1( flength is as much as is usually cast at one tmathe ornament first drops from the mould, all 0 ; n tocomposition is pared away with a knife, and tin - ,jq je d' 1 '

copper towards a fresh supply for the next cas • ot'

r - - wooden, „fter

for

jet

„t least

This composition is ** eqaa \ly " e

-lead,

o» e

I 01 Wit'tw

irding to t'>eP”J 8 OP

ments when formed, are glued upongrounds, or they are affixed by means of whitewhich they are painted or gilt, accor” 'which they are intended. This comp-eer, t. cheaper than carving, and in most cases is -calculated to answer all the purposes of that art. coU ldIt were much to be wished, that the art of P las ! e J r, e .. a j? a,n brought to its ancient perfection. dn ay and'buildings, the plastered walls and ceilings crack an115 /p, U I? time ’ S row damp, or moulder to decay. 0 f tin 9I he Romans had an art of rendering their s0 n *°

kind much more firm and durable ; and there is »°despair of reviving this art by proper trials. to

this

iur > e9

— r..© --r * 1 nresc* T

The ancient plastering of these people, p ^ gT mJ^jjtime, where it has not met with violent ^ f r ee

from accidents, is still found as firm and 0 n t * 10 ^ tli fi

cracks or crevices, and as smooth and P olls j gideS 0face, as if made of marble. The bottoms