866 MOSAIC 



ings always, as being a mixture of sand and mud, and pit-sand generally, as 

 being scarcely over "without a portion of clay, should bo washed before they are 

 used ; which is seldom necessary with river-sand, this being cleaned by the flowing 

 water. 



' I have ascertained by repeated experiments that 1 cubic foot of well-burned 

 chalk-lime fresh from the kiln, weighing 35 Ibs., when well mixed with 3- cubic 

 feet of good river-sand, and about 1 cubic foot of water, produced above 3 cubic 

 feet of as good mortar as this kind of lime is capable of forming. A smaller propor- 

 tion of sand, such as two parts to one of lime, is, however, often used, which the 

 workmen generally prefer; both because it requires less time and labour in mixing, 

 which saves trouble to the labourers, and it also suits the convenience of the masons 

 and bricklayers better, being what is termed tougher, that is, more easily worked, but 

 it does not by any means make such good mortar. If, on the other hand, the sand be 

 increased to more than the above proportion of 3J, it renders the mortar too short, 

 that is, not plastic enough for use, and causes it also to be too friable, for excess of 

 sand prevents mortar from setting into a compact adhesive mass. In short, there is a 

 certain just proportion between these two ingredients which produces the best mortar, 

 which I should say ought not to be less than 3, nor more than 3|, parts of sand to 

 1 of lime ; that is when common chalk-lime, or other pure limes, "are used, for diffe- 

 rent limes require different proportions. When the proportion of sand to lime is 

 stated in the above manner, which is done by architects as a part of their specification 

 or general directions for the execution of a building,- it is always understood, when 

 nothing is expressed to the contrary, that the parts are by fair level measure of the 

 lime, and by stricken measure for the sand ; and the lime is to be measured in lumps, 

 in the same state in which it comes from the kiln, without slaking, or even breaking 

 it into smaller pieces." Pasley. 



MORTAR, HYDRAULIC, is the kind of mortar used for building piers or 

 walls under or exposed to water, such as those of docks, &c. See HYDRAUIIC 

 CEMENT. 



MOSAIC. (Mosaiquc, Fr. ; Mosaisch, Ger.) There are several kinds of mosaic, 

 but all of them consist in imbedding fragments of differently-coloured substances, 

 usually glass or stones, in a cement, so as to produce the effect of a picture. The 

 beautiful chapel of Saint Lawrence in Florence, which contains the tombs of the 

 Medici, has been greatly admired by artists on account of the vast multitude of pro- 

 cioiis marbles, jaspers, agates, aventurines, malachites, &c., applied in mosaic upon its 

 walls. The detailed discussion of this subject belongs to a treatise upon the fine arts, 

 but the progress of the invention is so curious that some brief notice of mosaic-work 

 in general will not be out of place. 



When, with his advancing intelligence, man began to construct ornamental articles 

 to decorate his dwelling, or to adorn his person, we find him taking natural produc- 

 tions, chiefly from the mineral kingdom, and combining them in such a manner as 

 will afford, by their contrasts of colour, the most pleasing effects. From this arose 

 the art of mosaic, which appears, in the first instance, to have been applied only to 

 the combination of dice-shaped stones (tessera) in patterns. This was the opus 

 musivum of the Romans ; improving upon which, wo have the Italians introducing 

 the more elaborate and artistic pietra dura, now commonly known as Florentine 

 work. It is not our purpose to treat of any of the ancient forms of mosaic-work, 

 further than it is necessary to illustrate the subject before us. The opus tcsselatuin 

 consisted of small cubes of marble, worked by hand into simple geometrical figures. 

 The opus scctile was formed of different cruets or slices of marble, of which figures 

 and ornaments were made. The opus vermiculatum was of a far higher order than 

 these : by the employment of differently-coloured marbles, and, where great bril- 

 liancy of tint was required, by the aid of gems, the artists produced imitations of 

 figures, ornaments, and pictures, the whole object being portrayed in all its true 

 colours and shades. 



The advance from the opus vermiculatum to the fine mosaic-work, which had its 

 origin in Rome, and is, therefore, especially termed Roman mosaic, was easy ; and 

 wo find this delicate manufacture arising to a high degree of excellence in the city 

 whore it originated, and to which it has been almost entirely confined, Venice being 

 the only city which has attempted to compote with Rome. To this art-manufacture 

 we more especially direct attention, since a description of it will aid us in rendering 

 intelligible the most interesting and peculiarly novel manufacture of mosaic rug-work, 

 as practised by the Messrs. Crossleys. Roman, and also Venetian enamels, are made 

 of small rods of glass, called indiscriminately paste and smalt. In the first place, 

 cakes of glass are manufactured in every variety of colour and shade that are likely 

 to bo required. These cakes are drawn out into rods more or less attenuated, as they 

 aro intended to be used for finer or for coarser work, a great number being actually 



