"The Art of Intarsia"
by William Grundke

Part Four

Let's Make an Intarsia
   I have quite often heard the exclamation, "If only I could do something like that!" Now, here is the chance to make an actual intarsia like the one of the sailboats shown in the color photo of the jewelry box.
   A minimum of tools and money are required for this project. As far as equipment is concerned, you need only a small trim saw; a grinding wheel, such as used in cutting cabochons; a sanding drum; polishing wheel (buff); and a flexible shaft unit or motorized handpiece. If you have a combination unit for cutting cabochons, you will have the setup for sawing, grinding, sanding and polishing. If not, a trim saw plus a grinding head or other arbor arrangement on which wheels can be interchanged will do the trick.
   As far as optional equipment, a flat lapping machine would be handy, but not necessary. As mentioned previously in this series, lapping can be done by hand with silicon carbide and water on plate glass. This technique was covered in detail in the article. Polishing Stones by Hand which appeared in the January 1982 issue of this magazine. It would even be possible to do final smoothing and polishing by hand, eliminating the need for a sanding drum and buff. However, the power equipment with abrasive and polishing wheels make the work easier.
   For the flexible shaft unit or motorized handpiece (Fig. 6 in Part One of this series) you will need some Mizzy wheels (described under Grinding in Part Two of the series) and some separating discs (Figs. 5 and 13, Parts One and Two). OF course, if you already have some diamond or silicon carbide carving tools for use in the motorized handpiece or flexible shaft unit, they could certainly come in handy.
   Also optional would be a slab saw, if you prefer to cut your own gemstone slabs. This is probably the least needed of the machinery because many fine slabs are available from rock shops, from mail order suppliers, at gem and mineral shows, and through swapping with fellow rock hobbyists.
   The basic techniques for creating this intarsia will be found in the first three installments of this series which have appeared in this magazine - Part One, December 1981 issue; Part Two January 1982; Part Three, February 1982. Before starting this intarsia, be sure to study these before proceeding on this project.
   The first chore is to select a subject and draw a pattern. If you like the sailboat picture on the jewelry box, Fig. 22 is the author's full-size pattern. Note that this diagram includes extra waves as compared to the picture o the color photo. The number of waves you include are optional.

Figure 22

   When the pattern is made, number the various sections, which will be the different units of the intarsia. In Fig. 22, Unit No. 1 is the sky, Units 2, 3, 4 and 5 the sails, etc. Make several photocopies of the pattern so that you may cut out the images of the various units and glue them to the gemstone slabs (see Part One).
   Suitable gem materials that could be used include: verde antique, Oregon sunset-colored marble and blue lace agate to mention a few. For the jewelry box intarisia this writer used:
Sky - marble
Boats and sails - glass slag of various colors with howlite for white stripes
Top wave - blue lace agate
Next two waves - blue-green quartz of varying shades.
   As mentioned in Part One, I prefer slabs of ¼" thickness. Other intarsia workers find 3/16" to be thick enough. The choice is yours, but the extra thickness gives you more leeway in lapping. As can be seen, you will need a fair size slab for the sky. Make it large enough to allow plenty of margin around the pattern outline (wider and higher than the area enclosed by the wavy lines in Fig. 22). This is especially important if you are using soft material, such as marble employed in the sky of the intarsia pictured. If there is not enough margin, some of the cuts to make the recesses for the sail units can get too close to an edge of the stone and cause the slab to break.
   The slabs for the sails are actually constructed of several slabs. Note in the color picture that the sails are composed of stripes of different colored material (slag and howlite in this case). Figure 22 shows the widths of these stripes. Trim saw slices to these widths from slabs of the desired colors. Grind slight bevels on the back edges of these slices (Fig. 16, Part Two) and cement them together (Part Three) to create "constructed slabs." Flat lap the tops of these slabs. When you cut the unit parts from the pattern photocopies keep each sail (nos. 2, 3, 4 and 5) intact. Cement the sail patterns to the "constructed slabs" so that the stripes on the pattern line up with the stripes in the slabs. Cement the other unit patterns to the appropriate stones.
   Trim the slab for the sky across the bottom, a little below where the first wave will join it. Then use the trim saw to make 4 straight cuts along the mast lines. These cuts are designated A, B, C and D in Fig. 23. Next make diagonal cuts E, F, G, H, I, J, K, L and M (Fig. 24). Bring these close to the curved outlines of the sails (follow one of the techniques covered in Part One to avoid undercutting). Use a screwdriver or similar tool to break out the material between these cuts. Cuts L and M will automatically release the unwanted stone portions. To review this sawing and breaking away technique, refer to Fig. 8 and the accompanying instructions in Part One.
   Now, following the instructions accompanying Fig. 7 (Part One), use the saw blade to make notches and remove the material between the notches, in order to get closer to the outlines of the sails. Then, also as detailed with Fig. 7, swing the stone against the periphery of the saw blade to do minute grinding and remove still more material, getting even closer to the outline. Be sure to apply light pressure so that the blade will not catch the gem material.

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Figure 23. . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 24

   Note in Fig. 24, that an area (N) must be cut out for the prow of the forward boat. Follow the same techniques to accomplish this.
   Bring the sail openings completely to the outline with a Mizzy Wheel (see Part Two) chucked in a flexible shaft unit or motorized handpiece. Use a separating disc to clean out the corners (refer to instructions accompanying Figs. 5 and 13, Parts One and Two). Be sure to follow the safety precautions listed in Parts One and Two for using Mizzy wheels and separating discs. When this work has been completed, the sky slab should look like Fig. 25 (the dotted lines are final trim lines). Various carving points and wheel could also be used for this procedure.
   Now, shape the unit for sail No. 4. After trim sawing the preform, the outside curve can be done on a conventional grinding wheel (silicon carbide or diamond) for cabochon cutting. Grind carefully until this unit fits perfectly into its opening in the sky unit.
   Note that none of the sails or other units are overly large. Whenever possible, keep units small.
   This picture is small enough that an intarsia press is not needed for the cementing sequence. Instead, as described in Part Three, use a plywood board with wooden edging strips on two sides. Be sure to put two layers of wax paper on the plywood.
   Place Unit No. 1 (the sky) face down on the wax paper. Apply epoxy to Unit No. 4 (sail) and fit it into its proper recess in Unit 1. Push them against one of the edging strips and hold the, in place with aluminum push pins. AS mentioned before, the length of the pins depends on the thickness of the slabs and the hard ness of the plywood. Put under a heat lamp until the epoxy has completely hardened.
   Skipping to Fig. 30 we see a sky unit with sail units fitted in, being held in place on the plywood while the epoxy sets. This picture also shows another procedure, to be discovered later, which required the use of finishing nails as well as push pins.
   After the cement has hardened, you will undoubtedly find that some of the epoxy has gotten onto the face of the assembled unit. While it is still warm from the heat lamp, cut this epoxy away with a single-edge safety razor blade. This saves a lot of grinding time.
   You have now combined two units to make a lager unit. Lap the face of this assembly (see Part Two) until it is smooth to the touch. Use either 220 or 400 grit silicon carbide abrasive, depending on the qualities of the stones.
   Saw and shape Sail Unit - 2 and 3. Epoxy them into Unit No. 1, just as you did with Unit No. 4 After the cement dries, lap the face of the unit assembly until smooth.
Now for the last Sail Unit - No. 5. Shape it, epoxy in place and lap.
   As can be seen in Fig. 22, there are four sea gulls in the sky and for pennants on the boats. Openings must be cut I Unit No. 1 (sky) for these. To start, drill eight small diameter holes at the spots marked by dots in Fig. 22. In soft gem materials, drilling can be done with silicon carbide steel bits. For harder materials, you will need a gem drill (refer to books such as Specialized Gem Cutting which can be purchased at rock shops or ordered form mail-order suppliers).
   Next lay the unit assembly face down on a flat surface and grind around the holes with a Mizzy wheel. This is to thin the slab at the locations where the gulls and pennants will be to make the next operation easier. I thin the stone I these areas to about 1/8" thickness.
   To cut out the gull and pennant openings, I use a jeweler's saw with a No. 3 blade. The blade is fitted through a hole and locked in the saw frame. A slurry of 220 grit loose silicon carbide abrasive and water is applied to the area of the cut, and the jeweler' saw worked back and forth. The teeth of the saw blade pick up the grit and an opening for a gull or pennant is cut out. Now it becomes apparent why thinning the back of the slab in these areas is very helpful. For this type of work I have also used one of the diamond wire saw blades which are offered by rock hobby suppliers. The results were highly satisfactory.

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Figure 253 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 26

   Now comes a tricky part. The tiny pieces for the pennants and gulls must be cut and ground to shape to fit into the appropriate recesses. My method for making a pennant piece is to cut a length of stone somewhere between 1' and 1 ½" long. This piece has a triangular cross section which also tapers (see Fig. 26A). The triangular face on one end is smaller than the opening in the sky unit while that at the other end is larger. When you slip this piece through the face of the sky unit into the appropriate recess, it slides in until the cross section area of the correct dimensions is reached and the pennant stone fits snugly in its opening. Epoxy it in place.
   I made sea the gull pieces the same way, only they have a V-shaped cross section. When all; the pennant and gull pieces have been fitted, and the cement has dries, their excess lengths can be removed with a cutoff wheel or they can be ground away until just about flush with the surface of the sky unit. Lapping will bring them exactly flush.
   If this fine work sounds like a bit much, there is an alternate, much easier method. Simply crush small amounts of gem materials of the appropriate colors for the gulls and pennants. Mix this stone powder with epoxy, set the sky unit face down on wax paper and flow the epoxy mix into the correct locations. Allow to dry. Shave away the excess epoxy from the face of the unit.
   The tops of the masts can also be done with an epoxy-stone powder mix. If you choose to follow this procedure, it would be advisable to do them before the pennant openings are cut, otherwise, the nix for the pennants would flow into the mast slots.
   The other was to do the masts would be to cut and grind fine strips of stone. These would have to be ground and/or lapped down to the necessary narrow width. Probably they would have to be attached to blocks of wood or other suitable material with dop wax or an adhesive that you could easily dissolve. Sodium silicate (water glass) could be used as an adhesive. Apply it, attach the stone to the block, let set until hard and complete the grinding or lapping. Soak in warm water to dissolve the sodium silicate. Duco or similar household cement is still another alternate; it will dissolve in acetone. (Note: Use acetone in a well ventilated area and avoid inhaling the fumes. T0 prevent skin irritations, some people find it advisable to wear rubber gloves. And, some individuals who are allergic to acetone should probably avoid it altogether.)
   The next procedure is to cut and shape the boat hull pieces - Nos. 6, 7 and 8 - then cement them together into a unit. Epoxy this unit to the top unit. After the cement dries, lap the assembly.
   Now cut and shape wave pieces 9, 10 and 11. Cement them together to form a unit, then epoxy this unit to the rest of the intarsia. Let set until the cement is hard, then lap. If you wish to add more waves, as shown in Fig. 22, repeat the procedure.
   The intarsia is now assembled. The next procedure is to trim it on the three sides of the sky unit and on the bottom, bringing it to its final dimensions. If this trimming had been done previously, probably the sky piece would have cracked near the termination of the mast on Unit No. 4. Round the corners on a grinding wheel or with Mizzy wheels, what have you.
   Lap the face of the whole intarsia. I started with 220 grit and followed it with 400 and 600 grits. As discussed in Part Two, depending on the gem materials, one might find it necessary to start with 400 grit.
   I then worked the face of the stone picture on a drum sander, just like a flat cabochon. This was possible because it was a relatively small intarsia. I started with 400 grit wet sanding cloth and finished with 600 grit. This publication advises that all sanding be done wet to avoid inhaling dust composed of silicon carbide and stone particles.
   Polishing was done on a hard felt buff with a slurry of tin oxide. Other craftspersons might prefer a different buff/polish combination.
   If you wish to mount an intarsia in the lid of a jewelry box, as I did, craft and hobby shops stock wooden boxes such as this. Cut an opening in the lid of the appropriate size and shape. I added a piece of wood underneath, which is somewhat larger than the opening, to support the intarsia and hold it more securely.
   To decorate the sides of the box, why not cut some thin slices of stone and cement them on? Lap and/or grind, sand and polish them.

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Figure 27 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 28

Special Techniques
   Figure 27 shows how the sky unit looks after the sail units have been cemented in place. However, note that there are some additions as compared to the intarsia in the jewelry box. Masts have been attached to the sails, there is a circle and "arrow" design on the large sail and pennants have been embellished with circle decorations (dots).
   To make a mast, the flat side of a stone slice was cemented to a sail. The other side of the mast piece was then sawed and ground to the correct dimensions (it could be lapped).
   For the decoration on the sail, a hole was core drilled in the sail stone. A piece of stone was ground to a circle of the correct size and epoxied in. You could also cut the round stone with a core drill that has an inside diameter to match the outside diameter that was used to make the hole in the sail.
   The openings for the arrow design were made as described with the pennants and gulls. Don't forget to thin the sky unit in this area.
Figure 28 is a back view of Fig. 27.Note that a piece of scrap stone was cemented to the top of the sky unit to add strength in the area of the mast terminations.
   Perhaps, instead of putting the intarsia into a box lid, you would prefer to use it just as a picture. In this case, brass strips can be added to the sides to give it a finishing touch (don't round the corners). To set it off, you could mount it on a velvet background within a picture frame as pictured in Part One. We'll discuss mounting methods in a subsequent installment.

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Figure 29. . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 30

   To attach a brass strip, apply a length of masking tape to the face of the intarsia with part of the tape projecting beyond the edge of the stone. Stick the brass to this projection a shown in Fig. 29. Apply epoxy, raise the brass strip up to the edge of the intarsia, set the intarsia on the wax paper-covered plywood and push it against the wood edging strip. Figure 30 illustrates how everything is held snuggly in place with aluminum push pins and finishing nails driven into the plywood.
   The sailboat intarsia is good for a beginning project. After having completed such a work, one should be ready to try something more detailed, which we'll get into in the next installment.

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