This section is from the book "Turning And Mechanical Manipulation", by Charles Holtzapffel. Also available from Amazon: Turning and Mechanical Manipulation.

The blocks, when finished, are allowed to dry for some weeks, and are ultimately cut into thin veneers, and glued upon round boxes. Octagons of different patterns are united side by side, and the spaces filled in with right-angled triangles, so as to constitute straight patterns for the centers and borders of rectangular boxes. Small round sticks are occasionally turned into little ornaments, and the curvilinear surfaces so obtained, present various pretty effects when the intersections are accurate.

The compounded sections of the wooden mosaics are generally prepared beforehand of small triangles, as adistinctprocess, and are frequently screwed fast in cauls of their appropriate angles, or they are built up as laminated sheets, and cut into form with the saw.

The chequered squares are prepared from slips of veneer one inch or more wide, so as to avoid handling the little squares, which could scarcely be tied up in true rectangular arrangement. The pieces of veneer are glued together, either white and black alternately, or in any arrangement that the pattern may require; strips cut off the edges of the laminated pieces and reversed as at a, fig. 747, produce the chequered squares, cut obliquely and alternated they produce rhombuses b; and striped rhombuses c, triangles d, and squares, can be also readily obtained, and the author suggests that b, c, d, and similar pieces, should as in the diagrams, figs. 745 and 746, be mingled with the present patterns, many of which are much elaborated, principally from small triangles alone, without a sufficient regard to the general design or drawing of the figure. The author possesses however, a very good specimen of mosaic work composed almost entirely of triangles, which in a diameter of 3 1/4 inches, contains no less than 808 separate pieces of wood, combined with very good effect.

The square wood mosaics, called also Berlin mosaics, from their assimilation to worsted works, arc more recent than the triangular. Figures of vases, animals, and running patterns, are composed entirely of little squares of various coloured woods, which are glued up like the chequered works. Supposing the entire pattern to constitute a rectangle composed of 20 squares in width, and 30 in length, 30 slips of veneers of appropriate colours and an inch wide, are first glued together, and this is repeated 19 times, making one laminated block a, for every line of the figure. A veneer b, is then cut off from each of the 20 blocks a; and these striped veneers b, are glued side by side to constitute the group c, of 600 slender squares; the thin leaves cut off from the end of this last constitute the mosaic pattern D.

The accuracy of the work greatly depends on the exact similitude of the veneers as to thickness; and as the blocks a, will each produce some 15 or 20 repetitions of b and c, the persevering care required in the formation of a single specimen, will also effect a vast extent of repetition of the same pattern or d.

The small square mosaics for borders and other works are usually inlaid in slips of holly as running patterns, by aid of the buhl saw. Very large mosaics are usually made in 6, 9, or 12 sections, glued up separately into squares, and then combined. One example, thus formed by Mr. Burrowes, represents the Prince of Wales's feathers, arms, and motto; it measures 3 1/2 by 2 1/2 inches, and consists of between 8000 and 9000 squares; the block was prepared in 12 sections, that were afterwards united.*

* From the researchs of Winkelmann, Wilkinson, and others, there appears to be no doubt but that. 3300 years ago, the ancient Egyptians were wonderfully successful in making mosaics of minute cylinders, squares, and filaments of glass, united by partial fusion and pressure; and that from the end of the mass, slices, about one-sixth of an inch thick, were cut off and polished, much the same as above described.

Various specimens are referred to, in which the pictures are said to be very perfect and exactly alike on opposite sides, showing them to run through; the mode of construction is apparent, from the joinings being just visible in a strong light, and from the colours having in some places run into one another, from the partial excess of the heat employed in uniting them.

The Egyptians also appear to have made other mosaics, by cementing pieces of glass, stone, and gems on backgrounds, just the same as since practised by the ancient Romans, and by the artists of Italy and other countries in our own times. - See Wilkinsons Manners and Customs of the Ancient Egyptians, 1835, Vol. iii. pages 94 - 97, etc.

In sawing the regular prisms of from 3 to 12 sides, it is necessary the inclined beds should meet the saw-plate, at the same angle as that at which the sides of the polygon meet, or their exterior angles. It is therefore proposed as an example for all prisms, to trace in fig. 748 the formation of the hexagon, or 6-sided prism, from a round or irregular piece of wood, upon which, as a preparatory step, one plane surface has been cut in any manner, either by the saw or plane. The following table contains the several angles required.

In regular prisms of.. | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 sides. |

Their external angles measure .... | 60 | 90 | 108 | 120 | 12/ 4/7 | 135 | 140 | 144 | 147 3/11 | 150 deg. |

The supplements to the external angles, or what they fall short of 180 degrees, are... | 120 | 90 | 72 | 60 | 51 3/7 | 45 | 40 | 36 | 32 5/11 | 30 deg. |

Referring to the above table it is seen the external angle of the hexagon is 120 degrees (represented by the dotted arc A), and that the supplement to the latter is 60 degrees, therefore the inclined bed should also meet the saw at an angle of 60 degrees (represented by the dotted arc, B,) by means of this bed alone, the second side of the prism would be cut on the piece of wood. But in cutting the remaining four sides, it would be required to introduce some guide, to ensure the parallelism and equality in width of the sides; and this is done by laying a second angle upon the first, also equal to the supplementary angle of 60 degrees (represented by the dotted arc, C,). Then B, and C, which are of the same angle, together constitute a trough, and the width of the side of the trough near the saw, must be equal to the side of the required hexagon; but the second piece C, is not adjusted to its position, until after the first two sides of the prism have been sawn. The angle of the inclined beds must be very exact; as any error that may exist, becomes accumulated, or is six times multipled in producing a hexagon.

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