The attractive glass tankard has some damage, but that is usually related to the quality of the production process in the days when the glass was made at the end of the 17th century. The quest for clear glass in those days was not always so simple. Lead oxide was added to the glass to make it clear, but the chemical process had not yet been refined. The explains the hair cracks and the flaking of the glass.

The treatment

A number of elements in the damage were significant for the restoration. First and foremost, the glass surface displayed hair cracks with some loose flakes in between. Furthermore, the belly of the tankard showed several glued breakages, cracks, and gaps. The old glue had now turned yellow and the fragments had not been glued adjacently or smoothly. Moreover, the entire surface was very dusty and the hinged lid was kept separately.

During the recent treatment, restorer Nicole Minten cleaned the entire glass surface with demineralised water and ethanol. Moreover, the intention was to disconnect the glued breakages and glue them again. Immersion in solvents was not considered due to the fragile glass surface. The old adhesive joints would be dissolved by compressing with dichloromethane, but it emerged after examination that presumably a dual-component adhesive had been used which responded only moderately to this treatment. The compressing was sufficient to clean the surface, but not to disconnect the pieces. Moreover, it emerged from the examination that the fragment edges had already been sanded to fit better into the glued section.

And so, disconnecting and re-gluing proved to be impossible in this case, but the glass is certainly a lot clearer. The gluing joints are also less disruptive than before the treatment. The loose section of the lid were fastened back onto the ear. That assignment was carried out by the company Metafose, which specialises in the conservation and restoration of metal art pieces.