"The Art of Intarsia"
by William Grundke

Part Three

Cementing
   As has been mentioned in the previous chapters of this series, to assemble an intarsia picture, individual shaped stones pieces are cemented together to form units. Smaller units are then bonded together to form larger units, and so on until the picture has been completed.
   For this work I use and advise the use of 220 or 330 Epoxy. For snow scenes I prefer the 330 because it does not yellow as much. But, for most of my work I use the 220; it sets more slowly, and I find it to be stronger.
   To make cemented joints less obvious, the epoxy is colored with polyester resin pigments which are available at craft stores and other outlets that sell the resin. Mix the proper pigments with the epoxy to get hues that will match the colors of the stones as closely as possible. These pigments are dissolved in liquid. You will find that the colors and the liquid separate after the bottles stand for several days. I pour off the excess liquid and use the remaining paste only to color the epoxy.
   Some craftspersons use colored epoxy for another purpose. In some patterns it is desirable to show fine dividing lines, such as spaces between fingers on a picture of a person. These craftsmen add black pigment (or an appropriate color) to epoxy and fill the space(s).
   In certain tight areas this writer uses another type of colored cement. Small pieces of the appropriate gem material are powdered and added to epoxy, which is then flowed into the tiny area.
   Before cementing the stone pieces together, remove and paper patterns. I shave them off with a sharp knife. Since they are adhered with Duco cement, some craftspersons use acetone to dissolve the adhesive. Remember to use this solvent in a well ventilated area and avoid inhaling the fumes. If you, like some others, are allergic to acetone, wear rubber gloves, or don't use it at all.
   Be sure that the stone pieces are clean and free of any oils, such as saw coolant. They can be washed in detergent and hot water, then rinsed. Or a solvent, such as acetone, can be used.
   I use a palette knife to mix and apply the epoxy. A double thickness of wax paper is laid down on a flat surface (more about the type of surface below), and the cemented stones are placed face down on the wax paper. To speed up the setting of the epoxy, a heat lamp is positioned over the work.
   The surface on which the cemented pieces are placed while the epoxy hardens must be flat and level. Some artisans use a piece of plate glass, others a board. As mentioned above, the surface should be covered with a double thickness of wax paper; epoxy will not stick to it.
   With larger intarsias, there is another aspect to consider in cementing. Because epoxy shrinks somewhat, a picture can become warped. Therefore the author designed and uses an intarsia press (Fig. 17). The one pictured was made from a piece of ½" plywood (the work surface) to the bottom of which was cemented a piece of 1/8" masonite. Along two intersecting sides on the top are strips of ¼" x 1" oak strips for the stonework to butt against.

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Figure 17. . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 18

   Running along the short sides of this press are pieces of aluminum channel to which lengths of hardwood are attached. In these hardwood pieces were drilled 7/32" holes into which 20 thread ¼" x 1 ½" thumbscrews were threaded. The wood pieces can be moved back and forth and swiveled to different angles (see Figs. 19 and 20). Then the thumbscrews are gently tightened on the intarsia, holding it tight on the work surface.
   Figure 18 shows one of the wood pieces with the thumbscrews. Note that the pieces of aluminum channel were drilled through the bottom, first with a hole that would accommodate a ¼" bolt. Next a larger hole was drilled in the bottom leg of the channel through which a countersink was run to bevel the hole in the upper leg for the flat head of the bolt. Wing nuts on the bolts permit the hardwood bars to be locked in place.
   In Fig. 17 you can see how a groove was made in the edge of a short side of the press to provide a track in which the aluminum channel pieces slide. This grooving can best be done with a carpenter's table saw, but could be accomplished with a hand saw. Or other methods could be worked out.

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Figure 19 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 20

   Figures 19 and 20 show the press from different angles to illustrate how it is used. Instead of using a press, some craftspersons prevent their intarsias from warping by using different types of backings - plaster of Paris, cement, epoxy resin with a filer, stone slabs, etc. These methods will be reviewed in subsequent section.
   It is essential that stone pieces being cemented together tightly so that the joints will not be noticeable. This is why the plywood work surface of the intarsia press has wood strips on two sides; the stones are butted against these strips. The epoxy is applied to the edges of the stone pieces, they are placed face down on the wax paper on the plywood work surface, pushed against the wooden strips and held tightly in place with aluminum push pins and/or finishing nails. For a source of the push pins, check stationary stores, draftsmen's supply outlets or hardware stores. Those with aluminum heads are essential; the plastic type would melt under the heat lamp. The pins are available in 3/8" to 7/8" lengths. Which ones to use depends on the hardness of the plywood and the thickness of the stones.

Figure 21

   Figure 21 shows some intarsia units being held against a wooden strip on a plywood base. Both the push pins and finishing nails are being used. The press in not needed here because the unit is not large enough to worry about warpage. Smaller pictures can even be done without employing the press.
   The work surface shown in Fig. 21 is a piece of ¾" plywood to which were glued two strips of ½" x 1" wood (on adjoining edges of the plywood to form a 90 degree corner).
With the stone pieces pushed together snugly, very little cement will remain between the adjoining edges, but epoxy is strong and there will be enough. Also, as shown in Fig.16 in the previous chapter in this series, remember that the edges on the undersides of the stone pieces were slightly beveled. When the pieces are fitted together, these bevels form channels into which the epoxy squeezes. This strengthens the bond.
   This covers the basis of making an intarsia. I the next part of this series we'll apply these techniques by presenting a pattern for an intarsia picture and giving a step-by-step instructions for creating it.

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