"The Art of Intarsia"
by William Grundke

Part Two

   This series began in the December 1981 issue. Subjects covered in the first installment included: what is an intarsia, selecting a design and making templates, important characteristics that should influence the choice of gem materials, and sawing. All this was accompanied by color pictures of a number of the author's intarsias. Now to continue, let us consider:

   Lapping is the finishing of a flat surface. It is a process that takes place at several intervals during intarsia making, so we'll review it now.
   My method is to use a standard lapping machine) available at rock shops and from mail-order suppliers) with a revolving metal plate. A mixture of loose silicon carbide abrasive and water applied to this plate and the gem material worked back and forth across it (Fig. 9). I usually start with 220 grit abrasive, but as mentioned in the first installment, may begin with 400 grit if a gem material that undercuts is being worked. In the first several lapping sequences just 220 grit is used (or 400, if that is required). When the picture has been completed a normal procedure is to progress from 220 through 400 and 600 grits. Later, we'll discuss the question of polishing.
   If you so not have a aping machine, this work can be done by hand on a piece of heavy plate glass or a sheet of pig iron or cast iron. It takes a little longer, but the results are satisfactory.
   If you are unfamiliar with this type work, detailed instructions wee given in the series, Handbook of Flat Lapping by Robert Hill Sr., which appeared in this magazine in November and December 1977, and in the January, February, March, April, June, July, August and September 1978 issues. The subject (including lapping by hand) is also covered in the book, Specialized Gem Cutting which is sold by Mail-order firms and at rock shops.
   Parts of pictures or small intarsias may be ground flat on diamond discs. You'll find information on this subject in the book, How to Use Diamond Abrasives to Cut Gemstones by Arthur L. "Art" Riggle (also available from rock hobby suppliers).
   There are other types of equipment that can be used to finish a completed picture. We'll discuss those when we come to that sequence.
   Often, my first lapping sequence follows slab sawing. If a gemstone slab(s) shows saw marks and/or pits, I lap it with 220 grit (or 400, as the case may be) until the surface of the stone is nice and smooth.
   Not infrequently it is found that required lapping grinds away desirable color areas. Stones thus affected are discarded before any extensive work is done on them.

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Figure 9 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 10

   In putting together an intarsia, individual pieces of gemstone re shaped and cemented together to form units. These units are then bonded together to form larger units, working outward from the center of the design until, eventually, the complete picture has been put together. For instance, perhaps you wish to make a picture with a building against a setting of some trees, mountains and the sky. One unit might be the siding of the building, another the roof, still another a tree, etc. As they are completed, they are joined together and more units are added. In subsequent installments of this series, we'll show you just how this is done by covering the steps, from start to finish, for completing intarsia - the sailboat picture and the winter farm scene which are shown at the bottom right and top right on page 15 of last month's issue.
   When a unit is completed it is lapped (220 or 400 grit only). Then, each time units are cemented together, the assembly is lapped again, and so forth until the picture is completely assembled and the final lapping sequence is commenced.
   Returning to the subject of shaping, in Part One we told how a great deal of this work can be done with a trim saw. In fact, a technique was covered in which minute grinding is actually done on the saw blade's periphery. Even if this done, shaping must be completed on some form of grinding wheel. A regular silicon carbide wheel can be employed, but this writer advises that you must be the only one using it. A diamond grinding wheel, if available will not wear unevenly, and it will last a long time.
   The gemstone pieces are ground to the template outline. To insure proper fit with other pieces, the edges must be made absolutely perpendicular to the sides. If you are using a silicon carbide wheel or a peripheral diamond wheel, and your hand is steady, you may be able to do this on the periphery. Or, with a silicon carbide wheel, you can grind on the side (Fig. 10). Just be sure that adequate water is applied; this may require that a stream be directed to the wheel side.

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Figure 11 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 12

   Instead of peripheral wheels, many gem cutters use flat diamond grinding discs. One of these works well for producing the perpendicular edges. In Fig. 11, a diamond disc has been mounted on a horizontal arbor. In front of it is a grinding table with a miter gauge that was borrowed from a woodworking saw. This setup makes it possible to grind straight edges easily. If such a devise is not available, there are many other ways in which a do-it-yourselfer could rig up a steady rest.
   The larger grinding wheel and discs, such as used for cabochon cutting, will suffice for some shaping, but if there s fine detail work (which there usually is), some special tools are going to be needed. All of my intarsias have been made with the help of a motorized handpiece (Fig 12A) with a variety of carving points and wheels. A flexible shaft unit (Fig 12B) will also do excellent work.
   Among the accessories that I use with the motorized handpiece are Mizzy Wheels. These are actually miniature grinding wheels which are much employed by gemstone carvers. They are used dry, so work in a well ventilated area and wear a dust mask.    Better yet, is a dust collection system, such as found on many jewelry polishing machines. Also, when working with these wheels and other carving accessories, we strongly advise that you wear safety goggles or other eye protection.
   Mizzy Wheels measure 7/8" in diameter by 1/8" thick. They wear away fairly rapidly, but don't discard the small remainders; these come in handy in a number of spots.
   Diamond carving tools come in a variety of shapes and types. Some that I find useful are miniature grinding wheels, straight routers or cylinders, and saws. The miniature saws, or slitters, are used for applications like cutting and cleaning out corners, making slits, etc. The use of such tools will be found in books on gemstone carving which are sold at rock shops and by mail-order suppliers.
   Although they are not used for shaping, diamond drills are sometimes employed in intarsia work. There are solid and core types which are used to make holes where needed. Core drills can be also used to cut cylindrical pieces of stone.
   Besides diamond drills, metal tubes, running in a slurry of abrasive grit and water are used to make holes. The subject of drilling is covered in books such as Specialized Gem Cutting, mentioned previously.

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Figure 133 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 14

   Last month in Part One, we mentioned silicon carbide separating discs (Fig. 13). In addition to making narrow cuts, these can also be used for cleaning out corners and similar operations. To make a fine abrasive wheel, I apply some epoxy to one of these discs, sprinkle on some loose diamond grit and adhere another separating disc to the first one. Do not use too much epoxy or you will end up squeezing out the diamond abrasive. Let the assembly set until the epoxy has cured. Three separating discs bonded together in this manner make a good cutting tool.
   Remember that separating discs, like Mizzy Wheels, are used dry, so be sure to wear a dust mask and/or use a dust collection system. Also, remember that these discs are rather fragile and can fragment into flying pieces if twisted or pinched. Wear goggles or safety glasses when using them.
   Whatever type equipment you use for shaping, grind only to the template outline. Check frequently to be sure that adjoining pieces fit together exactly.
   In addition to very accurate grinding, I have another technique that helps to insure a close fit.A slurry of 220 grit silicon carbide abrasive and water is applied along the edges of two adjoining pieces that have been shaped. The pieces are then rubbed up and down against each other (Fig. 14) until they mate perfectly.

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Figure 15 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 16

   Pieces must sometimes be so small that they are difficult to hold for grinding. A solution to this problem is to cement the template to a piece of gem material large enough to handle. Next, saw and grind one edge to the outline. Follow this same procedure on the stone that will be adjacent to the piece you have just worked. Cement the two stones together (Fig. 15), then work one of them to the desired shape using the other as a handle. Repeat the process on the adjoining piece. If both stones together are too small, cement them to a third.
   When pieces have been shaped and fit together snugly, their undersides are beveled slightly. These bevels are on what will be the back of the picture. When the stones are cemented together, they are placed face down on a flat surface covered with wax paper. The bevels then form grooves (see Fig. 16) into which the cement flows. The width and depth of the groove in the drawing are exaggerated for illustrative purposes. A width of about the thickness of a piece of paper is all that is necessary. The depth should be controlled; if the bevels extend too far up the edges of the stone pieces it is possible to grind into the grooves during lapping which would have open areas in the picture.
   With shaping and beveling completed, the stone pieces are ready to be cemented together. We'll take up that subject next month in Part Three.


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