IVORY 1039 



3. Green dye. This is given by dipping blued ivory for a little while in solution of 

 nitro-muriate of tin, and then in a hot decoction of fustic. 



4. Yellow dye is given by impregnating the ivory first with the above tin mordant, 

 and then digesting it with heat in a strained decoction of fustic. The colour passes 

 into orange, if some Brazil wood has been mixed with the fustic. A very fine un- 

 changeable yellow may be communicated to ivory by steeping it 18 or 24 hours in a 

 strong solution of the neutral chromate of potash, and then plunging it for some time 

 in a boiling hot solution of acetate of lead. 



5. Red dye may be given by imbuing the ivory first with the tin mordant, then 

 plunging it in a bath of Brazil wood, cochineal, or a mixture of the two. Lac-dye may 

 be used with still more advantage, to produce a scarlet tint. If the scarlet ivory be 

 plunged for a little in a solution of potash, it will become cherry-red. 



6. Violet dye is given in the logwood-bath, to ivory previously mordanted for a 

 short time with solution of tin. "When the bath becomes exhausted, it imparts a lilac 

 hue. Violet ivory is changed to purple-red by steeping it a little while in water con- 

 taining a few drops of nitro-muriatic acid. 



With regard to dyeing ivory, it may in general be ooserved that the colours pene- 

 trate better before the surface is polished than afterwards. Should any dark spots 

 appear, they may be cleared up by rubbing them with chalk ; after which the ivory 

 sBould be dyed once more to produce perfect uniformity of shade. On taking it out of 

 the boiling hot dye-bath, it out to be immediately plunged into cold water, to prevent 

 the chance of fissures being caused by the heat. 



Aniline dyes. Any of these colours give a fine and permanent colour to ivory. 



If the borings and chips of the ivory-turner, called ivory dust, be boiled in water, a 

 kind of fine size is obtained. 



Ivory made flexible, Ivory articles may be made flexible and semi-transparent, by 

 immersing them in a solution of pure phosphoric acid of sp. gr. 1*139, and leaving 

 them there till they lose their opacity ; they are then to be taken out, washed with 

 water, and dried with a soft cloth ; it thus becomes as flexible as leather. It hardens 

 on exposure to dry air, but resumes its pliancy when immersed in hot water. Necks 

 of children's sucking-bottles are thus made. 



The following account of the methods of preparing this material, we extract from 

 Holtzapffel's ' Mechanical Manipulation ' : 



' On account of the great value cf ivory, it requires considerable judgment to be 

 employed in its preparation, from three conditions observable in the form of the tusk : 

 first, its being curved in the direction of its length ; secondly, hollow for about half 

 that extent, and gradually taper from the solid state to the thin feather edge at the 

 root ; and thirdly, elliptical or irregular in section. These three peculiarities give 

 economy, as the only waste should be that arising from the passage of the thin blade 

 of the saw : even the outside strips of the rind, called spills, are employed for the 

 handles of penknives, and many other little objects ; the scraps are burned in retorts 

 for the manufacture of ivory black, employed for making ink for copper-plate printers, 

 and other uses, and the clean sawdust and shavings are sometimes used for making 



jelly. 



' The methods of dividing the tooth, either into rectangular pieces or those of a 

 circular figure required for turning, are alike in their early stages, until the lathe is 

 resorted to. The ivory saw is stretched in a steel frame to keep it very tense ; the 

 blade generally measures from fifteen to thirty inches long, from one and a half to 

 three inches wide, and about the fortieth of an inch thick ; the teeth are rather 

 coarse, namely, about five or six to the inch, and they are sloped a little forward, that 

 is, between the angle of the common hand-saw tooth and the cross-cut saw. The 

 instrument should be very sharp, and but slightly set ; it requires to be guided very 

 correctly in entering, and with no more pressure than the weight of its own frame, 

 and is commonly lubricated with a little lard, tallow, or other solid fat. 



' The cutter begins generally at the hollow, and having fixed that extremity parallel 

 with the vice, with the curvature upwards, he saws off that piece which is too thin for 

 his purpose, and then two or three parallel pieces to the lengths of some particular 

 works, for which the thickness of the tooth at that part is most suitable ; he will then 

 saw off one very wedge-form piece, and afterwards two or three more parallel blocks. 



' In setting out the length of every section, he is guided by the gradually-increasing 

 thickness of the tooth ; having before him the patterns or images of his various 

 works, he will in all cases employ the hollow for the thickest work it will make. As 

 the tooth approaches the solid form, the consideration upon this score gradually ceases, 

 and then the blocks are cut off to any required measure, with only a general reference 

 to the distribution of the heel, or the excess arising from the curved nature of the tooth, 

 the cuts being in general directed as nearly as may be to the imaginary centre of cur- 

 vature. The greater waste occTirs in cutting up very long pieces, owing to the differ- 



