"Discovering A Lost Art Form"
by Conrad Grundke

Learning Commesso, Part I

5. Layout Process:
   a. Use a color photocopier to reduce or enlarge the original picture to the actual size of the "Commesso/Intarsia" you want to make.

   b. Lay tracing paper over the picture and trace the outlines of the final sections that will be required. This line drawing, Fig 2, will be the major tool from which you will be working. Make 10 paper template copies of the line drawing. Make an additional line drawing copy onto transparency film. I us a Personal Computer and Adobe Photoshop for these steps.
   c. Lay the transparency film pattern over a slab to find the section of the slab that you want to use. The advantage of the transparency film is that you can readily align the stone to find the potential section that will best satisfy your need. Being able to see the entire stone through the transparency film facilitates the selection.

   d. Cut sections out of the paper templates with a Xacto knife to form a template for each required piece of rock or rock assembly, Fig 3. Discard the cutout sections. In the past the cutout sections were glued onto the rocks and used as a cutting template. This method does not allow for the necessary accuracy since oil, water, and deterioration of the paper affected the usability. Orient the template over the stone slab located with the transparency film in step 6,. The template will further allow you to verify the effectiveness of the selected stone. I then trace the outline with a black Sharpie Ultra Fine Point Permanent Marker. Repeat for each section. You can generally get about three sections per sheet, Fig 4.

Cutting out sections of the paper template and placing the openings over your slabs helps determine the best parts to use.

6. Cutting & Fitting:
   a. You may need to modify the picture slightly to minimize the assembly and fitting process. I use the following definition to assist beginners. A "positive fit" is when two pieces of the picture can be placed faced down on a flat surface and they can be brought together for gluing without having to lift one of the pieces off of the surface. A "negative fit" requires one of the pieces to be lifted above the level of the other piece and dropped in place. A "positive fit" allows one to correct for errors by additional removal of material on the matching edges when fitting because there is extra material on the other end of the piece. A "negative fit" must be exact and if too much material is removed, there is no means for correction and a new piece must be restarted.

The recommended sequence for assembling the Mountain Retreat commesso/intarsia ensures that all the stones will come together in positive fits.

   b. To illustrate this consider the recommended sequence in Fig 5, as compared to a sequence of 8, 10, 11, 12, 13. In this alternate sequence stone #9 could not slide into place without lifting it and dropping it in place due to the church eave. A much more difficult assembly process. In the recommended sequence, stone #9 can be fit by sliding it into place from the left. In fact, the recommended sequence will eliminate all "negative fits" in this Intarsia.
   c. Only cut the side of the stone that is going to be fit and epoxied to another stone. You will grind up to the outline on the other edges at later stages. The intent is to always glue two large pieces together and then cut and grind one down to the desired size. The large piece will support the desired small piece, as it is being ground to size.
   d. Cut the edges so that they are a 90-degree angle from the top surface. Avoid undercutting, which leaves gaps that will fill with epoxy and can eventually distort your surface as the epoxy dries and shrinks. Undercutting will also expose larger and larger gaps as the picture is lapped down during assembly.
   e. I always finish the last grinding for a fit using a dremel tool with various bits as needed. Generally, it is imperative that you have two key considerations when using diamond tools; Keep 'Em Cool, and, Use Only Light Pressure. On all other pieces of equipment I stress that the students maintain a good supply of water to keep the tool cool. However, water on slabs that are being fitted for an intricate "Intarsia" will prevent seeing the fit, so I use all my dremel tools dry. Using light pressure and exhaling while grinding and inhaling with the tool away from the stone helps. Blowers and masks with filters are also very beneficial.
   f. The technique for getting a good fit between two stones is the same one that dentists have used as far back as I can remember. Mark the contact points between the upper and lower teeth with carbon paper and grind away the areas that touch, until most of the surface is touching. I suggest using "mental" carbon paper because the use of actual carbon paper has been tried and is too crude and time consuming. Holding the pieces up to the light and determining where the pieces touch is the most common technique. Using a light box is also viable. In either of these cases you must be sure to look directly through the crack between the pieces since a poor alignment will case the rear of the stone to block the light and give the indication that the pieces are touching when in fact they are not. At times by rocking the pieces together you can identify the point of contact.

A nibbling saw is used to cut an odd shaped piece with outside curves.

   g. A process called "nibbling" can be used for forming odd-shaped pieces. Our nibbling saw is simply a trim saw blade mounted on a grinding wheel arbor. For an outside curve, make straight cuts as close to the outline as possible. This leaves less material to be removed when grinding the final shape. To create an inside curve, use the saw blade to make straight cuts from the edge of the stone up to the outline, then cut diagonally to remove the projections. Use hand tools to make the final shape.

   Having located the necessary stones and laid out the areas to be used for the various sections, you are ready to begin assembling the Commesso/Intarsia. Part II discusses epoxying and then goes through the necesarry steps to complete the picture. It also explains a method for framing the the finished picture for showing in one of your club shows. Normally, beginners can spend several weeks locating stones for this project, depending on their supply of stones and access to dealers or other sources of raw and cut materials.

   For a copy of the paper template for the Mountain Retreat Commesso/Intarsia, contact Conrad Grundke at 2214-B Via Mariposa E., Laguna Woods, CA 92653; (949) 587-0935; e-mail: cgrundke@dslextreme.com.


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