An additional use of ornament lies in its employment to break joint, that is, to conceal the junction of the pieces of which any portion of the work is composed. For this purpose, the position for the joint is arranged so that one portion of the work that is turned to a plain edge, abuts against a moulding turned upon another, or, when the moulding is of bold proportions, some of its members may be turned upon each of the two pieces, when in either case the position of the joint is lost sight of. Want of sufficient length or diameter in the material, also sometimes renders a joint indispensable in a straight or curved portion of the work, in a position where the form requires the outline to be left plain, and where therefore the joint would be visible.
A joint in such a position may be fairly concealed, by means of a shallow bead or other ornament turned upon the edge of one piece, and only sufficiently deep to leave its most prominent member just level with the surface or outline of the work; which surface ornament, something like a level string course in architecture, causing little or no depression does not materially interfere with the outline. Incised ornament of this character is frequently employed when there is no joint, as in the Etruscan vases, figs. 670 to 678, when turned of small size and from single pieces of material. The lines indicated in these examples are the boundary lines of the colour on the surface of the originals, and are therefore appropriate even when the work is solid; but when it is of large size so as to require several pieces for its construction, the junctions would be made upon these lines of ornament, which then break or conceal the joint also.
Frequently a somewhat intermediate course is adopted, a band or moulding of inconsiderable height being turned to stand just above the plain curve; this, primarily serving to break joint, may also be rendered an effective ornament without greatly interfering with the outline. Thus the long curve of the amphora, referred to as deteriorated by the addition of any abruptly projecting curve, will when necessary submit to that of a thin band or fillet, the two edges of which may also be appropriately enriched with small and delicate mouldings. This expedient has been carried still further in the base of the candelabra, fig. 746; not however in this case to break joint, but to counteract the abrupt effect of the junction of the feet with the vase forming the center of the base.
The beauty of a long, well proportioned, uninterrupted curve in the outline is indubitable, but the form, the height or diameter, necessary to the purpose of the work, may render a single curve undesirable; mouldings are then appropriately employed to divide it. In some forms approaching the cylindrical character, the same curve is repeated on either side of the moulding serving the last purpose, or to break joint; but in most forms, the moulding terminates one and then serves as the starting point for a different curve. The moulding usually placed at the junction of a straight shaft with other portions of the work, such as the capital of the column referred to, becomes indispensable when a plain stem supports the body of a vase, or other work of globular or oviform section; the tapering moulding interposed then leads the larger to the smaller of these dis-similar forms, and avoids the disagreeable effect of an abrupt transition.
The character and proportions of the mouldings used and a suitable variety, the other points referred to, are again influenced by individual taste. Inelegance however, may easily arise from too frequent repetition; from errors in the separate shapes, the hollows, rounds and other forms employed; from incorrectly grouping these as members of mouldings and from ill-judged position. Repetition of the same ornament, but differing in magnitude upon different portions of the work, will be met with in many of the examples, and this is correct and desirable as giving unity to the design; but on the other hand, if the repetition be too frequent the effect is monotonous. When many mouldings are necessary, relief is afforded by the introduction of others, sometimes themselves repeated, interspersed among those previously referred to.
Mouldings not intended as exact reproductions of classic models, allow some latitude in the relative proportions of their different members, but every member should be carefully turned to the exact form it is intended to represent. Thus, and enumerating those most used in turning, the bead, indicated by fig. 597, the astragal, a bead standing between two fillets fig. 598, and the reverse of these, the cavetto or hollow, fig. 599, lose in effect, when in place of the true semicircular section, they are represented by inaccurately rounded forms. The quarter round and quarter hollow in like manner should be exactly quadrants of circles; these as in figs. 600, 601, are frequently terminated by the surface or cylindrical face of a fillet.
The ovolo, employed in similar positions to the .. quarter round and its reverse or concave form figs. 602, 603, may be considered for explanation, as composed of one half of the quarter circle forming the quarter round, with the other half replaced by a curve of longer and flatter sweep. Actually it is formed by portions of ovals, being fairly represented by the last joint of the thumb viewed edgewise, whence it is popularly called the "thumb moulding." The relative proportions of the two parts of this continuous curve may be almost indefinitely varied, nearly always with satisfactory effect; prominent as in a cornice, or standing alone as in the lip of a vase, any requisite increase in width may be obtained by extending the longer portion of its curvature. The ovolo may be terminated by a fillet, or by a quirk, as in the ogee fig. 607. The combination of a round and hollow in one curve forming the ogee, may have the two halves corresponding in dimensions, or their relative magnitudes may be considerably varied; either the convex or concave half may he placed above, the former ogee, fig. 605, being styled the cyma-recta and the latter the cyma-reversa.