"The Art of Intarsia"
by William Grundke

Part One

Silent Night

   On the cover, and on the two color pages that accompany this article, are examples of intarsia, the art of fitting pieces of stone together to form a picture. It is an ancient art form that was known in Roman days and reached a peak of development in 16th Century Florence, Italy. To the gem cutter it offers a challenge, for it requires imagination, visualization and skill. However, anyone who can cut cabochons and lap flat surfaces can learn how to do this work. Or if you have become involved in today's popular art of making channel jewelry (see article elsewhere in this issue), learning to cut the gemstones to fit into the channels is excellent preparation for intarsia making.
   By studying the color photos it can be seen how individual pieces of gem material were shaped and fitted into the appropriate areas of the intarsia pictures. Sometimes a design calls for pieces with straight sides - a geometric pattern fro instance; or an image in a picture, like a building, can require only straight cuts, sometimes strips with parallel sides. At other times outside and/or inside curves must be made. All of these techniques will be covered in this series.

Selecting a design
   The first requirement for an intarsia is a design or pattern. For the beginner, it is often best to start with a geometric design. The more straight lines it has, the easier the job will be. If you are fortunate enough to be artistically inclined, you can draw your own design. If not, you can find many ideas in publications, especially art magazines. I often use photographs that I have shot of beautiful scenes, buildings, etc. Other sources of inspiration are greeting cards and reproductions of paintings.

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   Designs can be traced if they are the right size. If they must be enlarged, or reduced, you can use the old method of drawing squares on the design and larger or smaller squares (whichever is required) on a blank piece of paper. Copy the picture by drawing the lines you find in the original in the appropriate squares on the copying paper. Be sure that your finished copy is a well-executed design with all the necessary lines and connections.
   If copying by drawing is unsatisfactory, you can have the design photographed with a camera which makes negatives. The negative can then be put in an enlarger and a photographic print of the desired dimensions made. Perhaps you have a friend who is a photographer, or this work can be done by many camera stores.

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   Still another possible method would be to use a pantograph, an instrument that operates on the parallelogram principle to copy drawings, etc., reducing or enlarging them as needed. Such devises are available at artists' and draftsmen's supply stores. The average type works reasonably well, but it is quite possible that some touch-up work will be required to make the design completely satisfactory.
   Whatever method you use, make duplicate copies of the design. Using a photocopy machine is very satisfactory. The duplicates are carefully cut apart to make templates for the component pieces.

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Figure 1 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 2

   Figure 1 shows a simple geometric design. To facilitate keeping track of the [parts, some craftspersons number the templates and their corresponding locations on the master drawings, as illustrated in Figure 1.
   When you cut out the templates, be sure not to cut off any part of the design, as this will result in a poor fit.
   The templates are adhered to the stones with a waterproof adhesive. I use Duco household cement. First an application of the Duco is used to attach a template to the appropriate piece of gem material. Next, more Duco is smeared on top of the template to give it a waterproof coating. Allow the cement to dry.
   In working with geometric designs, it is not necessary to use paper templates or tracings on all pieces. Instead the "direct measuring" method may be employed. Figure 2 shows a striped design made of stone strips of alternating colors. The simplest method for making the strips is to measure their width on gemstone slabs of the right color. A trim saw is then used to cut the strips. If any are too wide, they can be brought to exact measurement on a grinding wheel. (Sawing and grinding techniques are covered later.) When the strips are cemented together, they form a unit that can be shaped to fit its place in the picture.

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Material
   To create maximum beauty in an intarsia, you must have the right gem material for every piece. Select your stones carefully and keep these factors in mind:

1. Color - Before starting a picture, be sure that you have suitable colors for all arts and that the ones selected are compatible. One difficulty frequently encountered (especially when selecting background material) is finding enough stone of pure solid color. Though not a color, white is a good example. Lots of material looks white, but when cut, it comes out an off shade or it may have markings and inclusions. Experienced cutters have found that out of most accumulations of rough gem material, less than half is of suitable color.
2. Pattern - Look for patterns that may be utilized to advantage. For instance, in the intarsia of the Grist Mill shown on the first page of color photos, stones were found that had patterns which resembled the leaves on trees, grass, a mountainside and clouds. Dendritic material may be used to represent plant life while wavy patterns may suggest a seascape. Observe the other intarsias on the color pages and you will see how the patterns in various gem materials were used to advantage. By using your imagination and ingenuity, you can produce interesting and unusual effects.
3. Hardness - When the intarsia is assembled, its surface must be flat lapped. To minimize undercutting, try to select stones of the same or nearly the same hardness. This is easier said than done, however, so you must do the best you can. IF you do have materials of mixed hardness, one way to reduce undercutting is to start with a finer grit in the lapping process. I normally start with 220 grit silicon carbide abrasive, but when stones of varying hardness must be lapped, I often begin with 400 grit. If the area to be lapped is not too large, you might be able to do it on a flat diamond disc. This minimizes the problem because diamond abrasive, with its fast cutting action, cuts away harder and softer materials at about the same rate of speed.
4. Slab Thickness - The first cutting process for an intarsia is slabbing the stones. If you plan to purchase slabs, rather than cut your own, try to obtain a selection of       uniform or nearly the same thickness. This is not mandatory because the pieces are assembled face down which produces an event viewing surface. However, the more even the back surface is, the easier it is to complete the picture.

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Sawing
   If you plan to slab your own material, Point No. 4, above, still applies - try to make the slabs the same thickness. Most intarsia makers find a thickness of about 3/16" to ¼" satisfactory. When possible I cut my slabs about ¼" thick because the pictures I make require a great deal of lapping. When lapping is finished, the stones end up around 3/16" thick.
   Often I have a limited amount of a certain gem material with which I wish to cover a fair size area. I cut it into thin slabs, around 1/8" thick, then I back these by cementing on slabs of common stone, also about 1/8" thick. Basically, it's the process of making doublets, but often on a larger scale.
   After you have obtained the slabs, you will need a trim saw. A conventional model as depicted in Fig. 3, will work. However, because the arbor and blade center on this type is under the table, the curve of the blade cuts further into the underside of a slab (see drawing). On straight cuts, this is not a problem, but often the saw is used to cut straight into the gem material, make notches, etc. If the undercutting comes close to what will be the upper surface (in the face of the picture), it is possible to expose a cavity when that surface is lapped.

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Figure 3 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 4

   To minimize undercutting, you can make a wooden wedge on which one side is angled to align with the axis of the saw arbor (Fig. 4). A slot is cut in the wedge to accommodate the blade and it is set up as shown in the drawing. The slab is placed on the upper surface of the wedge and slid into the blade.
   We have discussed what can be referred to as conventional trim saws. There are other types on the market. For instance, there is the variety on which the blade is mounted on an arbor that is attached to an overhead swinging arm which brings the blade down to the stone. Some of these saws are combination units that will first slab a piece of material, then through the use of an auxiliary table, will trim it. If you have such a saw, check to see how the slab lines up with the arbor during the trimming operation. Undercutting may not be a problem. You might even find that the blade will cut farther into the top than the bottom of the stone. This could require a little extra grinding later on, but you would not have to worry about opening pits during lapping.
   Still other types of machines available are diamond band saws and diamond wire saws. These are specifically designed for cutting various shapes, including inside and outside curves. If you do not already have a saw, it is a good idea to check with rock shops and mail-order suppliers for the various types available. Factors involved include what you want the saw to do, how fast you want to do it, and how much you want to pay.
   A faceter's saw with a thin blade can also be handy for intarsia work. It can be used to cut thin slots like the spaces between fingers on an image of a person.
Instead of a saw, a separating disc (Fig. 5) can be used for narrow cuts. These discs are ofd a silicon carbide composition and are for attaching to small mandrels, as shown in the picture. A mandrel is then chucked in a motorized handpiece (Fig. 6A) of the handpiece of a flexible shaft unit (Fig. 6B).

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Figure 5. . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 6

   Separating discs are somewhat fragile and once in a while one will get twisted or pinched which can result in its exploding into fragments. This calls for protection. Be sure to wear goggles or safetly glasses when using one of these accessories.
   Also, since separating discs are used dry, there is rock dust which can be hazardous to your health. Work in a well ventilated area - and wear a dust mask.
For thin cuts I have used a jeweler's saw with a coarser blade, say a 2/0, and a mixture of 220 grit loose silicon carbide abrasive and water. Some of the grit mixture is applied to the area of the cut and the toothed saw blade worked back and forth against the stone. More grit is added as needed.
   If you have a quantity of strips with straight parallel sides, and all of the same width, to cut, a rip fence like those on wood saws can be devised. Be sure that this fence is parallel to the saw blade. If the saw is the type on which the gemstone slab is pushed into the blade this becomes especially important to prevent blade damage.
   There are some techniques for sawing out the pieces for an intarsia that will save much grinding time. Applying these techniques will be easier if you have devised some method to prevent undercutting.
   Curves, especially inside curves, are the greatest sawing problems if you have a standard saw with a circular blade. As mentioned, the diamond wire and band saws are designed for cutting various shapes including curves.
   A circular saw blade cuts in straight lines, but there are methods for using one to work curves. For an outside curve (Fig. 7), first saw straight lines as close to the periphery as you can. The projections left can be removed by lightly pushing them against the blade, sawing many little notches. Next the divisions between the notches can be pushed into the blade, and finally, you can swing the stone in a circular motion, actually doing minute grinding on the blade's periphery. Use very light pressure to prevent the blade from catching in the stone and becoming damaged. This technique requires much practice. Also, it may reduce blade life, especially if any grinding is done on the side which removes the "set." Intarsia workers usually feel the time saved is worth the extra blade wear.

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Figure 7 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 8

   Of course, after sawing the notches, and the areas between these notches, you can go to a grinding wheel. All the saw cuts reduce grinding time. If you have a diamond grinding wheel, this operation should be reasonably fast.
   To saw an inside curve (Fig. 8) with a circular blade, cut straight lines up to the outline (watch for undercutting). Next, make diagonal cuts to remove the projections left by the straight cuts. To remove the remaining small projections, follow instructions for the outside curve. It cannot be emphasized too much to use light pressure and hold the stone steady.
   The final small projections in an inside curve could also be removed with some form of carving tool or a rock router. These will be reviewed in the discussion on grinding in the next section.

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