44th Annual AIC meeting, May 17, 2016, "When in Rome, do as the Romans do? The Conservation of an Italian Marble and Micromosaic Tabletop” by Elizabeth La Duc

Elizabeth La Duc gave an engrossing talk in the Objects Specialty session on the conservation treatment of a 19th century Pietre Dure and micromosaic tabletop belonging to the Josiah Quincy house of Historic New England. The stone tabletop, positioned on top of a painting and gilded wooden base, had and been conserved in the past.  Her treatment was readdressing this past treatment and returning it to exhibit-able condition.
Pietre Dure translates into English as “hard stone”.  The Pietre Dure portions consist of decorative stones set into the carved channels within the black marble base and adhered with a rosin and beeswax.  The micromosaic areas are images made up from tiny tesserae called smalti.  The smalti are cut to shape and inserted into an adhesive of linseed oil, lime and marble dust.  The top surface was polished to a flat surface and the gaps between the tesserae were filled with tinted beeswax.  This beeswax can be seen under ultraviolet light, but it has often been lost through over cleaning and use.
The table top was in poor condition.  The four sections were poorly adhered and slightly misaligned.  A large crack in the stone tabletop ran across the middle of the tabletop and transected both the Pietre Dure and the micromosaic elements of the table.  Two stone inlays were missing and there were losses in the micromosaic along the central break.
The conservation treatment started with a surface cleaning of calcium saturated water with the pH raised to 8.5 with ammonia and added drops of Triton.  Acetone was wicked into the old joins to dissolve the older restoration adhesive.  B72 and microballons were used to glue the pieces back together.
For the conservation of the Pietre Dure portions two options were considered.  In Florence, the missing elements would have been replaced with new cut stone.  The Pietre Dure objects are decorative and require a high level of finish.  Another Italian treatment option is to cast crushed stone and resin to recreate the missing inlays.  This second approach was chosen and the new Pietre Dure elements were created with tinted epoxy bulked with fumed silica cast into silicone rubber molds.  In some areas it was necessary to back of the Pietre Dure areas of loss with a layer of Japanese tissue coated with B72.  The epoxy elements were then cast directly into the loss.  Gamblin conservation colors were used to finish off the top of these fills and a layer of Acrysol WS24 was brushed on top to give a polished shine.
The micromosaic repairs were based on similar micromosaic designs.  Since the micromosaics were mass produced with only a small range of designs, similar images could be used as guidelines for decorative elements on the fills.  The areas of loss in the micromosaics were backed with acid free matt board topped with a layer of modostuc.  Gamblin conservation colors were used to inpaint the surface in two steps.  The first step painted the background colors and the second step painted the individual small tesserae.
This was an elegant and well executed treatment with results that were aesthetically pleasing and reversible.  Under close examination, the areas of filled loss are distinguishable from the original material.  This was a great talk and I hope to get a chance to work on micromosaics someday!