Pottery is generally durable and stable, yet we find the need to intervene for a number of reasons; chemical analysis for dating, reconstruction of shards for simple display, stabilization of surfaces or environment to prevent deterioration, and fabrication of missing elements to enhance value or to conceal damages. It is these latter areas which are the concern of the conservator and the restorer.
16th century Chinese manuscripts give us recipes for adhesives for the repair of porcelain, which is a more problematic application due to its vitreous nature. Egg whites and glutinous rice, wheat gluten and lime, bamboo resin and egg whites are but a few of the suggested remedies. A standard work on household management published in England in 1861 gives recipes using brandy, gum mastic and isinglass (or even boiled Gloucester cheese combined with quicklime or orange shellac and rectified spirit for rebonding ceramics).
Some earliest repairs involves a large utility ceramic from Palestine, around 5000BC, where holes either side of the break were drilled and a leather strap laced through to bind the fracture. It was a simple utilitarian vessel, obviously at the time it was probably expensive and it was necessary to preserve or repair pieces and in that way avoid the purchase of a replacement. In more recent centuries where utilitarian objects have doubled as objects of both function and beauty, repairs serve the duel purpose of returning use and preserving aesthetic qualities.
The most widely used methods of mending ceramics in the last four hundred years are metal riveting, lacing and doweling. Riveting has its origins in China and found wide usage throughout Europe and the United States up to the middle part of this century. Metal clamp repair required considerable skill, as is obvious in the diversity of results. Unfortunately rivets often corrode and stain, breaklines also become soiled.
A rather curious procedure came along in the latter half of the eighteenth century called "china burning". A broken vessel was rejoined by applying a highly fluxed glaze or enamel to the break edges, then refired. The most bizarre aspect of this practice is that the china burner often signs the "mended" article. This process is irreversible.
One point of confusion that still may exist in the public’s mind is the difference between conservation and restoration. Conservation refers to the processes, which keep an object from harm, loss or future decay and simultaneously preserves the true nature of the object. "True nature" could be interpreted as evidence of origin (anything indicative of the making or process like firing faults or craze lines), associated materials which illustrate use (contents of a funerary urn or apothecary jar), or even subsequent historic modifications which are significant enough to preserve (engraved silver rivets or tea spouts, Japanese gold lacquer repair or ormolu mounts masking breaks).
A restoration desirable and honest if carried out to a discreet level where all original surfaces are visible. Fillers and paints would be applied within the confines of missing areas only. There would be no attempts to disguise inherent damages such as glaze faults, kiln damages or slumping. There can be no improvement on the original intent or fate of process.
In order to best reveal true nature and original surfaces, it would stand to reason that a lot of emphasis would be placed on cleaning. Often times overspray restoration through the use of an airbrush is carried out to mask stains, haircracks and simple breaklines.
This attention to cleaning processes often precludes the need for further, more invasive and costly repairs. Adhesives, particularly for use on porcelain, have always been a problem due to their yellowing and viscosity. There have been considerable advances in the use of epoxy resins for bonding and more importantly for matching "color fills". When properly manipulated and applied these materials give the restorer the ability to mimic depth, translucence and color when filling voids, glaze loss, rivet holes and chips specific to the areas of damage without obscuring original surfaces. It can also be used to imitate parian, jade and cloisonné. Hopefully, under the right conditions of after care we will see these applications lasting decades rather than years.