Last week I started the restoration of a marquetry panel on the base of an English tall case clock, made around 1700. This clock, like most of those clocks from that period, had lost its feet along with the lower 6" of the carcase, including the side panels. When it was last restored, in the 1920's, in London, the worker removed the surviving marquetry from the lower part of the panel and replaced the pine board underneath. Then he replaced the marquetry surface as best he could, saving most of the elements. He also replaced both side panels of the base, and added a double molded base where the round feet were.
Inside the case, I found a lot of powder post beetle damage, so I had the clock fumigated by a professional in a chamber for 48 hours with methyl bromide gas. Methyl bromide gas is the best way to guarantee full kill of the eggs, as most other fumigants kill only the adult and larvae, leaving the eggs to start the deadly process over once they hatch.
Here is the clock, with the sides removed.
I was fortunate to be a participant in an international group of marquetry restorers in Paris during the early 1990's. We called our group ADEN, which was a combination of the Musee des Arts Decoratifs de Paris and the Ecole Nationale Superieure Des Technologies et Industries du Bois, located in Nancy, France. We did a lot of research on modifying protein glues, age testing, rehydrating old glues, and other specific problems related to conserving old marquetry.
One of the papers published in March 1997 specifically discussed this problem of the clock: Amelioration des operations de recollage des placages et de redressement des panneaux-supports lors de la restoration de panneaux decoratifs. Short translation: how to restore old marquetry panels.
Out of this research came the idea to make and modify protein glues, which I used to develop Old Brown Glue. Although OBG is now sold nationally and used for a wide range of woodworking projects, I developed it originally to restore marquetry, which requires a long open time and deep penetration properties, as well as the ability to rehydrate and bond to old protein glue itself.
The first step is to place paper towels on the surface and add clean distilled water. Watch and wait a few minutes or longer for the water to soak into the mastic and under the loose elements. When you can see that the mastic has expanded and is raising up from the surface, you stop and remove the paper towels and surface moisture. Then you flood the surface with Old Brown Glue and rub it into the marquetry. Be careful to hold down all the loose elements while at the same time pushing the glue around, allowing it to suck under all the loose edges.
This method is usually done with the finish intact. It is not necessary or desirable to remove the surface shellac or finish for this to work. Note that the glue will penetrate only where the finish is damaged or lost, and only where the marquetry elements are loose or missing. That is one of the neat features of this process. You can conserve the original finish, if it exists and still reglue the marquetry in place.
Note I am holding down the floating loose elements with my left hand fingers while I am rubbing the glue over the surface with the right hand.
At the same time, I have heated an aluminum plate on top of a kerosene heater. I place two layers of clean newspaper on the plate and the lay the marquetry panel glue side (face side) down on the paper.
The heated plate cannot be too hot. If it burns your skin it will burn the glue. 150 degrees maximum.
Note that there are still pieces of paper on the new elements. This is also removed with cold water and gentle scraping. Once the surface is clean you can begin the process of coloring the new elements to match the old. Different chemicals, dyes and stains are normally used to balance the color and shellac is used to seal in the results. Here is the panel during the coloring process. It is not finished. I will glue it onto the clock and finish all the other small repairs before I complete the polishing, The original finish of the clock will be conserved with a French rubbing compound, called a "popote." When the clock is done, next week, I will post a final picture.
I hope this illustrates clearly how you can approach such a project with a systematically proven process. I am not the only person who uses this technique. I can assure you that many workers in Europe, both in museums and private practice, are using these methods on a regular basis. The goal is, of course, to conserve the great work of the masters for the future appreciation of collectors not yet born.
UPDATE: Here is a photo of the clock put back together, cleaned and polished with a fresh coat of wax.