The square cut, or trap cut, is the most simple form of cutting facets, and also serves as the foundation of the facets of the brilliant cut. The method of producing the trap cut will be therefore first described, and this will be followed by some observations on the brilliant cut. In order to avoid confusion, it will be more convenient to limit the majority of the examples to elliptical stones cut with eight principal planes or facets, one on each of the sides of an irregular octagon. Stones are frequently cut with as many as twelve or fourteen sides, but the general method is exactly the same, whatever may be the number of sides.

Fig. 1151 represents in plan, and fig. 1152 in side elevation, a stone cut on the face only with a single row or height of eight planes or squares connecting the central table with the girdle. In cutting this form, the stone is cemented upon a stick with the side to constitute the back outwards; this is then ground flat, the edge cut into shape for the girdle, and the back polished; the stone is then re-cemented upon the stick with the front outwards. The stick should be a little smaller in diameter at the end than the size of the stone, which requires to be placed exactly central on the stick, and with the flattened back as nearly as possible at right angles to the axis of the stick, in order that the table may be cut parallel with the back, and also that the squares on the top may be all cut at the same angle.

The cutting on the front of the stone is commenced by grinding the flat table; a uniform bevel is then cut around the top. The bevel is made of about the width of the desired squares, and is called a water basil, from its running uninterruptedly around the stone. So far the process is exactly the same as for cutting an elliptical stone with a bevelled edge.

The eight squares, or facets, are then cut upon the bevelled edge. For this purpose the stone is applied to the mill as shown in fig. 1150, the gim peg, h, being adjusted for position, until upon trial it is found that, on placing the stone fairly upon the lap or mill, and inserting the upper end of the stick in one of the notches in the wooden socket, the stick is inclined at the same angle as that at which the water basil was ground. The gim peg is then fixed by the wing nut beneath the bench, and the wooden socket secured by the wedge; the mill is then put in revolution, and the stone is applied, first to cut the two facets on the longest sides opposite to each other, and then those at the two ends are cut as nearly square as practicable, under the guidance of the eye alone; lastly, the four squares at the corners are cut to bring the stone to the octagonal form.

Fig. 1150.

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The four planes first cut at right angles serve as the basis of the figure, and some care and practice are required to place them exactly square, but the process is less difficult than might be anticipated, as in cutting the first pair of opposite planes, it may be readily perceived whether or not they are parallel, and should they not be correctly placed at the first attempt, the stick is slightly twisted in the hand for changing the position of the squares. But little pressure is exerted upon the stone, with the fingers applied above the stick and as near to the stone as convenient. The square position of the pair of planes at the two ends, may in like manner be estimated very nearly by a practised eye, and these foundation squares having been correctly placed, the position of the four squares at the corners is tolerably easy of attainment, and these squares are gradually enlarged until the desired figure is produced. In elliptical stones the corner squares are mostly smaller than the others, in order to avoid the reduction of the material. In cutting a stone with twelve squares on the same height, the four squares at right angles are first cut in the same manner, and the figure is completed by cutting two facets at each of the four angles, instead of one only as for the octagon. Stones with ten or fourteen facets on the one row are rather more difficult to cut by hand, as only the two opposite facets in the middle can be derived from the square figure.

Figs. 1151.

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Figs. 1153 and 1154 represent a thicker stone trapped in two heights, or cut with two rows of square facets, one above the other, and placed at different angles with the table of the stone. The row of squares adjoining the girdle is always left somewhat wider than that adjoining the table, partly with the view of compensating for the narrow portion enclosed in the setting.

The stone is prepared in exactly the same manner as for a single height of trapping, except that two water basils of the desired widths of the squares, are cut upon the top of the stone. The row of squares near the girdle is first cut, the cement stick being inserted in the same hole in the gim peg for cutting every square in the same row. The row of squares adjoining the table is then cut in the same manner, except that the stick is inserted in a higher hole in the gim peg, in order to place the squares at a greater angle; and some care is required to cut the upper row exactly opposite the lower.

As previously mentioned, transparent stones, that are of sufficient thickness, are generally cut both on the front and back. In this case about one-third of the entire thickness is given to the front, and about two-thirds to the back, as shown in figs. 1155 and 1156, which represent the side elevation and back plan of a stone trapped in two heights or rows of squares on the front, like fig. 1154, and three heights at the back, a style of cutting frequently adopted for small emeralds and other stones. Those of medium size have generally four heights on the back, and very large emeralds sometimes have three heights of trapping on the face, and from five to eight heights on the back; but with emeralds the trap cut is not often carried to the latter degree of elaboration, unless it be done with the view of keeping the gem as heavy as possible, as the greater the number of heights in the trapping, the more roundness can be given to the general contour of the back, and consequently greater weight to the stone; but if the convexity be too great, it detracts from the lustre of the gem.