Conservation and restoration of ceramic objects
[1] The cleaning, handling, storage, and in general treatment of ceramics is consistent with that of glass because they are made of similar oxygen-rich components, such as silicates.
[2] In conservation ceramics are broken down into three groups: unfired clay, earthenware or terracotta, and stoneware and porcelain.
The firing makes the clay water insoluble but does not allow the formation of an extensive glassy or vitreous within the body.
Due to its porosity, earthenware is susceptible to moisture and creates problems including cracks, breaks and mold growth.
To prevent this issue, many historic houses will line storage and display shelves with a thin layer of ethafoam (polyethylene foam) or bubble wrap.
Storing objects near windows, heaters, fireplaces, and exterior walls can create an unstable environment with temperature and humidity fluctuation and increase potential for damage.
Wool felt attracts and harbors insects including moths and silverfish which can be potentially very harmful to other collection material types.
Museum technicians, curators, and conservators are trained to prepare a moving plan before an object is even touched.
Although the intent was to repair the object for use or display, some dated practices are now known to increase damage either physically, from rivets or staples, or chemically, from formerly used adhesives that off-gas.
Differences can be seen to the naked eye due to discoloration, being matched poorly, and change in texture or gloss.
Removing previous filling materials, either mechanically or chemically, and replacing them with new fillers can help keep the piece strong and stable.
Saws, drills, and other mechanical methods can be used to remove the bulk of protruding materials; however, scratches, chips, and breaks can occur.
Dust and grease may be held on the surface loosely by electrostatic forces or weak chemical bonds and are easily removed.
Mechanical cleaning is typically much easier to control than chemical treatments and there is no danger of dirt being drawn into a solution and then absorbed by the ceramic.
Large ceramic vessels are cleaned with a delicate vacuum cleaner with a soft, muslin-covered head.
Picking and cutting is used when there is hardened dirt, encrustations, or old restoration materials closely adhering to the surface.
The dangers with these tools are the increase potential for scratches, gouges, cracking, and breaking of the object due to pressure.
Solid forms of abrasives include glass-fiber brush or a rubber burr on a dental drill.
For example, in 16th century China, people would repair broken ceramics by using pieces from other objects to disguise the patch.
The most common ceramics that need consolidation are excavated pieces because they tend to have lost their bonding fabrics due to leaching or absorption of soluble salts.
A consolidant works in two ways: it either links to the particles in the ceramic chemically or it may form a support system mechanically without reacting with the fabric itself.
[6] Although easily reversible, the relative ease with which the glue breaks down makes it a less strong bonding method.
Additionally research shows that the silica will better distribute stress and strain that occurs during evaporation of the solvent and during the setting of the adhesive film.
Conservators will cut through dowels with a piercing saw and soften the area with a solvent, like acetone to remove two pieces of ceramic from one another.
Plaster of Paris is a material that consists of calcium sulphate hemihydrate power and is produced by heating gypsum to 120 °C.
When mixed with water, an exothermic reaction occurs and forms a hard white filling similar to density of fired ceramics.
Different grades of plasters are available and vary based on their particle size, setting time, density, expansion, and color.
[4]: p.198 A thermoplastic synthetic wax resin mixture developed by John W Burke and Steve Colton in 1997 can be used to compensate losses in objects from translucent materials such as alabaster, marble, calcite, diorite, and anhydrite.
The mixture consists of polyvinyl acetate (PVAC) AYAC, ethylene acrylic acid (EAA) copolymers A-C 540, and 580, antioxidants Irganox 1076 or 1035, dry pigments, marble powder, and other additives which were all melted together.
The conservator prevents works of art from disappearing or loses its purpose whilst analyzing the complex stage of its material history and the cause of alteration.
