OBSOLETE FILL MATERIALS FOUND ON CERAMICS
Almost all the fill materials described in this article are no longer in use and should be considered obsolete. Most of the natural resins and waxes have poor or limited aging characteristics, and they discolor, becoming brittle and cracking, before deteriorating further. Other materials such as wood, gutta-percha, and metal (fittings or solder) are both physically incompatible and visually obtrusive. Moreover, they have often resulted in damage to ceramics in application or in attempts at removal.
Interestingly, one of the older techniques mentioned above has recently become fashionable again and may yet have a future. This is the recurring use of urushi, which has both a long history and excellent stability under good storage conditions. It is the subject of renewed interest in conservation studios in Japan and is currently taught there as a ceramics restoration technique. Collectors in the United States have also expressed an interest in having broken Japanese ceramics restored in this traditional manner. Unfortunately, the technique is difficult (and toxic) to work with and has an aesthetic appearance that is neither suited for everyone's taste (see fig. 7) nor appropriate for all ceramics.
The making of fired ceramic restorations has also recently been recommended as a “new” method for ceramic fills (Andreyeva 1995; Hogan et al. 1996), but, in this author's opinion, the technique should remain on the obsolete list. It requires a multistep process, involving casting and molding the original, making a template and throwing the clay on a wheel, firing the replacement pieces (or vessel), and then modifying the newly made vessel or ceramic fragments to fit. Creating a good fit (and join) is difficult owing to the substantial shrinkage, cracking, or distortion of the new clay upon drying (Hogan et al. 1996); after joining the old and the new, the irregularities must be filled. It is also difficult to justify the fabrication of a reconstruction that is more than 75% modern to insert a few fragments. A modern ceramic reproduction displayed alongside the original fragments would be more appropriate. Since there are other materials and methods available (Elston 1990b; Koob 1987) this technique seems to be both unnecessary and extremely time consuming.
Certainly some of the finer manufactured ceramic imitations and restorations done in the 19th century are worthy of preservation. They are a testament to the aesthetic and ethical approaches of the period. Suggestions that they be left on restored vessels, or possibly reused in treatment, are still subjects of much debate (Pavlukhina 1995). Tracing the development of ceramic restoration styles and the workshops with which they were associated could enlighten this debate. It has already been noted how different ceramics collections reflect the time at which they were restored as well as the influences of aesthetic taste and appreciation (Bousquet and Devambez 1950).
Loss compensation on ceramics is still an active topic of debate in the conservation field, particularly as to the extent of restoration. Not all broken or reconstructed ceramics require loss compensation, and the decision to fill losses should be determined on the basis of the eventual disposition of the ceramic, whether it be for museum or private display, study and publication, or archaeological storage. Other deciding factors include the current trends in aesthetics and restoration philosophy (Podany 1995).
It is logical to limit the amount of intervention that a ceramic endures and the types of materials that are used in its conservation (Koob 1991). Of paramount importance is preserving the integrity of the ceramic object through the use of predictable, dependable, easily usable, and reversible fill materials. The combination of materials and their potential differences in aging and interaction pose further problems for the stability of a ceramic. Even today, a restored ceramic may have so many different synthetic materials attached to it (Barov 1988) that it is difficult to predict when one will deteriorate or interact with another.
Fortunately, the experienced ceramics conservator now has an arsenal of solvents and techniques to aid in the removal of all of these resins, putties, and fills. Retreatment requires both the ability to identify the material and understand its chemistry well enough to remove it. Technical analysis and research by conservation scientists and polymer chemists have greatly aided the ceramics conservator in this area, so that these obsolete fill materials can be safely removed without risking damage to the ceramic (or to the conservator). Once the ceramic is returned to its fragmented state, the next step is to put the pieces back together. The restoration challenge begins again.
I thank Dr. Chris Maines, conservation scientist in the Scientific Research Department, National Gallery of Art, for the identifications of unknown resins. I also thank Julie Lauffenberger, conservator at the Walters Art Gallery, and Sidney Williston, head conservator at Mario's Conservation Services, for assistance in tracking down early references, and Hiroko Kariya, project conservator at the Brooklyn Museum, for the treatment and photographs of the bowl in figures 17–19.