"The Art of Intarsia"
by William Grundke

Part Six

Figure 32

Backing and Framing Your Intarsia
   In the past five installments of this series, we have presented the steps for completing an intarsia picture, starting with the selection of gem materials and taking the operation through the final surface finishing. When all this is done, it is time to prepare the intarsia for display.
   The project in the March 1982 issue was the making of a small gemstone picture to be set into the top of a jewelry box. An opening was cut into the top of the box to accommodate the intarsia and it was cemented in place. The addition of a wood backing piece to support the stonework completed the mounting of the picture.
If you wish to display the intarsia as you would a painting, putting it in a frame is an effective means. The way in which this writer frames such a work is shown in Fig. 32, which happens to be Silent Night, the cover subject of the December 1981 issue of this magazine. The intarsia is mounted on a velvet-covered backing piece which is fitted into a picture frame.
   The first step is to put a 5/16" wide brass edging around the intarsia as described in Part Five of this series (G&M, April 1982). This, in effect, is an inner frame.
   To attach the intarsia to the backing board, I use flat head bolts (machine screws), 1/8" in diameter and 5/8" long, with hex nuts. On each bolt, one edge of the head is ground flat to prevent it from turning in the adhesive with which it is attached to the intarsia.
   I use plastic steel epoxy for the adhesive, but regular epoxy or epoxy putty would also be satisfactory. The flat heads of the bolts are attached to the corners on the back of the intarsia with "globs" of plastic steel. Small amounts of the adhesive are built up over the heads to insure a strong bond. Figure 33 shows the back of Silent Night with the bolts in place. Figure 33A is a closeup of one of the bolts and the surrounding plastic steel.
   When the adhesive has set, a piece of paper is laid on the floor and the intarsia is set on it with the bolts projecting downward. The bolts are pushed through the paper, then a pencil line is made around the brass frame. This outline is transferred to a piece of ¼" masonite, and the bolt locations are marked through the holes in the paper. Holes for the bolts are drilled through the masonite at these spots. Depending on the individual intarsia, it may be necessary to countersink these holes to accommodate the bolt heads and adhesive. This was not necessary on Silent Night because the brass rim projects down far enough from the intarsia back that its edge is below the level of the adhesive and bolt heads.

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Figure 33. . . . . . . . . . . . ... . . . . . . . . . . . . . . . Figure 33A

   An area of the desired width for a border around the intarsia (refer to Fig. 32) is marked out. The masonite is sawed to size along this outline.
   The backing board is then covered with velvet. I select a piece of velvet of a color that will compliment the intarsia and cut a piece that extends ½" from all sides of the masonite. To attach the velvet to the backing board I use 3M Spray Adhesive. Coatings of this adhesive are sprayed on the back of the velvet and on the smooth face of the masonite, then allowed to dry. The velvet is attached by laying it down on the masonite, starting at a lower corner and working upward and outward. Use a wide soft-bristled paint brush of a soft cloth to smooth it out. This operation is a little tricky because when the dried adhesive o the velvet meets that on the masonite, here is an instant bond; it works like contact cement. Work carefully to avoid wrinkles. The excess velvet around the edges is cut off with a sharp knife. The bolt holes are cut through the velvet.
   The masonite is then put in a frame, just like you would with a picture.i use custom-made frames to achieve a good appearance. For hangin the picture I use the conventional combination of screw eyes and picture wire. I do not believe that the hook arrangements seen on some frames are strong enough for the weight involved here.
   Finally the bolts on the intarsia are pushed through the holes in masonite and the machine nuts are threaded on to hold the assembly firmly together. Figure 34 shows the masonite backing with velvet facing within the picture frame. The intarsia has been removed) its outline in the velvet is visible) so that the bolt holes can be observed. Figure 35 is a back view showing the rough side of the masonite, the nails holding it is place and the bolt holes.

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Figure 343 . . . . . . . . . . . . . ... . . . . . . . . . . . . . . Figure 35

Other Backing Methods
   The author has found the above backing method to be highly satisfactory. The purposes of backing are to give strength and to prevent warping. Using the cementing methods described in Part Three (G&M,Feb. 1982), including an intarsia press, if needed, and attaching the intarsia to a backing board work will fulfill these purposes.
   There are other backing methods, some of which have been used for many years. First, let us look art a modern technique. A thin, lightweight backing may be made with epoxy resin. Polyester resin (casting resin, etc.) is not satisfactory because it tends to shrink which will warp the intarsia. Epoxy resin had less shrinkage. Either glass cloth or fiberglass matting should be used as a filler.
   One method for applying the epoxy resin also provides an integral frame. The body of the intarsia picture is made of thinner gemstone slabs - 3/16" for instance. Slabs making up the border are cut 3/8" thick. (Or, if you prefer to use ¼" thick slab as this writer often does, the border could be done with stones 7/16" thick, of maybe even ½".) When the units are cemented together face down, there is a depressed area o the back. This area is filled with the filler (matting) and epoxy resin. The border pieces then form a natural frame.
   The techniques that follow also provide strong backings that will prevent warpage. They are traditional methods that have been used by many artisans, including those in Italy where intarisas have been made for centuries. However, they all have one disadvantage; they add considerable weight.
   One method is to make a backing of stone. IF the back of the intarsia is relatively even, it could be lapped smooth. However, if slabs of different thickness have been used, as is often the case, it is better to fill the resulting depressions with cement, plaster of Paris or epoxy resin (see Fig. 36). After filling, lap the back until it is flat.
   A gemstone slab large enough to cover the back may be difficult to find. If so, two slabs may be used. Or, you might use stone other than gem material, such as a slice of sandstone which can be purchased at a building supply outlet. Be sure that the backing stone(s) is flat, lapping if necessary. Cover its entire surface with mixed epoxy, then press the backing firmly to the back of the intarsia and let set until the epoxy hardens.
   For clean edges all around, you can cut a backing piece that is large than the intarsia. After it has been epoxied to the intarsia, it can be sawed to match the front.
   A variation, when using a stone backing, is to cut the backing to full dimensions for the finished picture. An intarsia of the image only - no background - is then made and attached to the backing. A polished gemstone intarsia against an unpolished material, such as a piece of sandstone, can provide an interesting contrast.
   The other traditional method is to make a backing of plaster of Paris or Portland cement. The intarsia is placed face down on a piece of glass and a frame of light sheet aluminum or other sheet metal is formed around it. The metal rim should be high enough to allow the finished product to be from ½" to ¾" thick. Another type of frame, made with strips of wood nailed to a wooden base, is depicted in Fig. 37. As an alternate, you can make a frame of brass or heavier gauge aluminum to be left on as a permanent decorative that will also reinforce the edges.
   For extra strength you may also place a piece of ¼" mesh galvanized wire screen on the back of the intarsia before pouring the backing.
   If you wish to use plaster of Paris (available at hardware stores, lumber yards, etc.), mix it with water according to the manufacturer's instructions. Apply a thick coat to the back of the intarsia (inside the frame as described above) with a paint brush. Allow to dry, then repeat the process day by day until the desired thickness is reached. This technique minimizes the shrinkage of the plaster to prevent warpage.
   Portland cement can be purchased at building supply house, lumber yards, etc. Mix it half and half with fine, clean, salt-free sand. First, however, mix a small amount of pure cement and water to a consistency of cream. Pour this mixture over the back of the intarsia until it is barely covered, then pour in the cement and sand mixture to a depth that will make the total thickness of stone and cement not more than ¾". It takes approximately 21 days for the cement to cure, and it should be kept most with a wet cloth so that it will not dry too quickly. Otherwise, it chalks and cracks.

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Figure 36 . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . Figure 37

Alternate Framing Methods
   If you wish to use a picture frame, instead of mounting the intarsia to a velvet covered backing, as the author does, you can simply use a frame that fits the intarsia. In that case, the stonework must be thin enough to coincide with the depth of the rabbet in the frame. Or, you can use a custom-made frame which allows for a deeper rabbet.
   Still another method preferred by some artisans is to frame intrasias with cloth matting. A visit to an art gallery or an interior decorator's would probably turn up even more ideas.
   To conclude our discussion of intarsia pictures, the next installment will cover some special techniques. Following it will be instructions for making intarsia cabochons.


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