Having worked with clay from a young age, I love seeing the diversity of ceramic objects in the Carlos’ collection. The range of techniques used throughout human history to form, fire, and decorate clay vessels and the similarities of techniques used across cultural lines is fascinating.
Due to the fact that clay is such an accessible medium for creating, ceramic objects can be found in every gallery at the Carlos, some of which include slip-decorated Nazca vessels, a glazed Roman chalice, an incised Makonde pot, and a highly detailed black figure Attic vase. Each object was formed and decorated in its own unique way; however, the similarities in materials and processes used lead to a number of shared condition issues.
There are two main ways a ceramic object can been built: hand-formed, created by pinching or coiling, or wheel-thrown. In some cases, objects have been made by a combination of these methods. Delicate elements like spouts, feet, and handles are often formed separately and then attached to the vessel before firing. Once formed, these objects are fired by exposing them to heat from the sun, fire, or a kiln. The firing temperature will affect a vessel’s strength and vulnerability to water (consider a terracotta flowerpot versus a porcelain teacup).
Modern-day potters and many cultures over the course of history have used a range of glazes to decorate ceramics. A thin slurry containing silica and a mix of other metal oxides is applied to the surface of the ceramic, and when fired, forms a vitreous surface layer. Depending on the contents of the glaze these can be either glossy or matte, colorful or colorless, thick or thin.
Another material used by clay artists to decorate ceramic vessels is slip. This is a liquid mixture of clay and water that can be applied to the surface of a ceramic and layered to add detail, as with the black figure Attic vase, or an object can be dipped in slip and burnished for a glossy finish.
In general, ceramics are much more durable than organic materials like wood, paper, or textile; however, their porosity and brittle nature expose them to other kinds of damage. While light and pests are less worrisome, ceramics are susceptible to water, soiling, and salt damage due to their porosity. The brittleness of ceramic also makes mechanical damage more likely.
Variability in the surface treatment of a ceramic can increase the risk of these factors. A glazed ceramic will be much less vulnerable to water and salts than an unglazed ceramic, for example. In your home, ceramic objects may include china sets, porcelain figurines, flowerpots, or your favorite mug. Understanding the materiality of ceramic objects and how to care for them can go a long way in preserving your treasures.
- Dust: Dust can accumulate on the surface of your ceramics and over time be more difficult to remove. Dust is hydrophilic, meaning it will attract moisture, which will cause surface grime to penetrate the ceramic and cause visual soiling.
- Temperature: While ceramics are stable in a range of temperatures, undergoing drastic temperature changes and freeze/thaw cycles can cause stress to the ceramic fabric. Over time this can cause cracking, delamination of the surface, or breaks.
- Physical stresses: Improper handling of ceramic objects can be the cause of severe damage. Contact with abrasive surfaces or fabrics that snag the surface can cause damage.
- Salts: In the presence of humidity, salt deliquesces (dissolves) and can be absorbed into the ceramic. When the humidity drops, salts recrystallize and expand inside the ceramic, causing stress to the ceramic fabric.
- Check ceramics for lead or uranium glazes before using for eating or drinking. These are more common in older ceramics (uranium was used as a colorant prior to WWII), although lead glazes are still used in many countries. If you are unsure or the glaze is damaged, there are at-home tests that can be used to detect lead.
- Avoid exposing these objects to extreme temperature changes. Bring flowerpots and ceramic objects inside during the wintertime.
- Avoid placing ceramics of value on shelves or surfaces that might be subject to vibrations. Dampen vibrations with polyethylene sheeting or place small bumpers around the object.
- Wash by hand whenever possible with water and gentle detergent and avoid using harsh chemicals to clean. Do not wash very porous ceramics.
- Regular dusting with a soft brush and vacuuming will go a long way in keeping your ceramics clean.
- Repair of broken ceramics is better done by professionals; do not try to repair your ceramic valuables with commercially available adhesives such as hotmelt, “super” white emulsions, and epoxy glues. These adhesives may fail or become brittle, yellow, or irreversible over time and are inappropriate for ceramic repair.
- Pick up the object with two hands, supporting the bottom. Never handle an object by the spout, handle, or rim only.
- When handling ceramic objects, avoid wearing jewelry or clothing that will scratch or snag the surface.
- Always handle with clean hands to avoid transferring unwanted oils.