This article, The Care and Restoration of Ceramics, was first published by the on-line magazine of ‘The Antiques Roadshow’ site: AntiquesAmerica.com. It was republished by the New England Journal in March 2002.

After receiving a degree in business from the University of Arizona, Roger Krokey pursued careers in chemistry and business planning, before his expertise in and appreciation of pottery as an art form led him to pursue the craft of restoration. He owns and operates Terra Nuova Restorations in Rhinebeck, New York.

This article helps answer some common questions about ceramic restoration.

What is the distinction between ceramic conservation and restoration?

In a generic sense, conservation is seen as the province of museum work and archaeological digs. Conservators do some repair work, but their emphasis is on process documentation, research, future study, and a repair methodology that does not change the object’s appearance overtly. While the term restoration can imply all of the above, its emphasis is usually one of making invisible repairs.

What makes a specific ceramic piece a good candidate for restoration?

Anything ceramic (fired clay) can be restored. That said, one must also take into account subjective issues – sentimental value, irreplaceable memories, and family harmony – as well as issues of practicality such as historical preservation, usability, and effect of resale value.

For example, the 17 pieces of delft Adam and Eve charger [Fig. 1] were purchased for $1,000. After a restoration cost of $800, it quickly sold for $2,500. The new owner, fully aware of the extent of the damage and resultant repair, was delighted with his purchase. The difference in monetary value between an object in perfect condition and one that has been restored is a judgement call by an appraiser or qualified dealer. It is based on two factors: (1) the extent of original damage and (2) the quality of the restoration.

Fig. 1. delft charger. Diam. 13". private collection

It is important to preserve minor age-appropriate damage. A restorer should always use a rubber frisket to mask raw edge chips on faience and delft, then remove it once restoration is complete. A shiny chip is a sure sign of poor restoration. Other examples of damage that should not be restored include original imperfections (e.g., crazing, pitting, and blistering) and kiln accidents such as glaze overmelt and attached chards from nearby pottery.

Molding missing applique, teacup handles, or even half the foot ring on the large delft bowl seen in [Figs. 2, 3, and 4] takes less time and makes for a higher-quality match than attempting to model the form by hand. Maintaining authenticity is important and may require research to determine the exact positioning of the missing element. Many objects were mass-produced and have been documented in reference books while others were a one-of-a-kind without any pictured source. This latter type requires collaboration between the restorer and an expert in that type of ceramic to create the most authentic repair.

How can restoration be detected?

Fig. 2. delft bowl (18th century0, cleaned and ready for assembly. H. 8", diam 15". private collection.

Fig. 3. Delft bowl's foot being molded. Private collection.

Fig. 4. delft bowl's foot and break damage restored and airbrushed white. Private collection

While some restoration is truly invisible, it can be detectable to those who

know how to look for it. When buying an antique, always ask if the object has been restored. If the answer is noncommittal, or if the seller does not know, as might be the case for a piece at auction, you can perform one or two simple tests:

• Tap the piece with your finger. A dull sound suggests it may have structural problems.
• Gently run a sharp implement (e.g., a razor, knife, or keys) over the glazed surface. If it slides smoothly, as though over glass, it is a fair assumption that it has not been restored. This test must be done with the owner’s permission, because it can scratch the surface. An object that has been through extensive repair (painted over) is likely to have received a final clear coat of acrylic enamel to protect the restoration. Both this clear-coated and untouched area will be hard to the touch, but the former will cause a razor blade to drag and mark its surface.
• Since most repairs involve edges, angling the object toward a light source will accentuate slight changes in level or differences in gloss.
• The human eye is extremely sensitive to the colors blue and magenta. If either color is present, examine it in sunlight. Restoration with a poor color match will be more obvious under harsh sunlight. Many paints used in ceramic restoration before the advent of colorfast paints & clear coats (1960) are now beginning to darken or yellow. Today’s restorers know this and insist on using only non-oxidizing and anti-ultraviolet materials.

Damage: What causes it and how to prevent it?

Most damage to ceramics is a result of physical shock rather than slow chemical or environmentally caused deterioration. To prevent an object from falling over during dusting, a cat’s nudging, or a mild earthquake, secure an adhesive putty to the bottom of the object then press it to the surface on which the piece is displayed. Adhesive putty is available at most hardware stores, where it is sold under numerous brand names such as ‘Handi-Tak’.

Unrestored items may be washed with half-strength liquid dishwashing detergent. Dislodge dust or stubborn dirt by using a quarter-inch painter’s brush. More aggressive cleaning or stain removal should be left to a conservator.

Don’t underestimate the danger inherent to the type of damage called hairlines or spiders. When sellers exclaim, “It’s just a hairline,” beware. These breaks in the clay body originate from thermal or mechanical shock and could eventually cause the piece to split in half. One sure way to create a thermal-shock hairline is to pour hot tea into a cold teacup. Even the heavier-bodied teapots are not immune. A restorer can easily stabilize a hairline to prevent further breakage.

A condition similar to hairlines but very difficult to repair is called springing. During firing, a ceramic object undergoes extreme stress and uneven heating. This builds tension into the item, and if broken or chipped, could result in a warped hairline or break. Each side of the split distorts, thus making perfect alignment impossible unless reintroducing stress with clamps or other tools during the gluing process. Plates, platters, and American salt-glazed crocks tend to be prone to this type of hairline.

One should take note concerning crazing (the tiny lines on the surface of some glazed objects), that is generally considered to be charming and appropriate with age. They form during the cool-down process while still in the kiln and in sufficiently severe cases can cause the glaze to flake (efface) from the body [Fig. 5]. Today, glaze chemistry is a science, but improper formulation can cause the glaze to shrink faster than the clay body. Control of this mismatch was achieved only in the twentieth century. There should be absolutely no concern about crazing if the glaze sounds solid when tapped gently with a fingernail.

fig. 5. Delft teapot with glaze effaced. H. 5". Private collection.

Two aspects of ceramic repair (gluing and bleaching) warrant mentioning. Each month several badly glued items are brought into my studio. If an object is broken and you intend to have it restored in the future, do not attempt to glue it yourself. If you use inappropriate glue for the type of clay or you misalign the pieces, the object will need to be taken apart before a restorer can repair it. Naturally, this puts the object at greater risk and the restoration work will cost more.

Peroxide is the agent most often used by restorers and museum personnel for bleaching stains. Common laundry bleach should not be used. It contains chlorine, which can remain in the clay and cause the glaze to detach. Most bleaching agents are hazardous. Improper use can leave some glazes with a permanent smoky appearance. Consult a restorer or conservator if you have any doubts. Their expertise in identifying the type of stain and an appropriate approach to bleaching can save you from ruining an object.

What can I expect from a ceramic restorer?

When you need a ceramic restorer, ask a respected antique dealer or museum curator in your area for a recommendation. Request to see examples of the restorer’s work and discuss his or her depth of experience with your type of ceramic collection. An ethical restorer will try to understand your needs as well as assess an approach that will be within your budget. Ask your restorer for an estimate of completion time. A busy craftsperson’s backlog can result in a turnaround time of three to nine months.

The restorer should explain your options so you can make an educated decision about the appropriate method of treatment. These can range from simply strengthening, or stabilizing, a hairline to a full restoration of the object. Usually restorers do not charge for estimates, but complicated projects that require some preliminary work to make an accurate estimate may entail some up-front cost.

A restorer should advise you what to expect in terms of appearance and durability once a repair approach has been decided. For example, dinnerware pieces are not ideal candidates for restoration; often they have become impregnated with grease, which weakens the paint bond and the restoration can be damaged with use

I am frequently asked, “Is this item worth repairing?” A restorer that is about to estimate a repair should not be asked this question; it can pose a conflict of interest. A qualified appraiser is the best person to determine an object’s monetary worth. An archaeologist or a curator in an appropriate area of decorative arts, on the other hand, should assess historical value.

With the advancement of invisible-repair technology, it is more vital than ever that business ethics and disclosure of restoration be held as paramount values within the antique dealing community. Restoration should always be approached with the intent to uplift an object’s worth, whether monetary, historical, or aesthetic.

Tips

• A dull sound when gently tapped with a finger can indicate a ceramic piece has structural problems.
• Original imperfections and minor age-appropriate damage should not be restored.
• To protect a displayed ceramic piece, secure a small piece of putty to the bottom of the object, then press it to the surface of the display case.
• Beware of sellers who diminish the potential problems of hairlines or spiders, which can cause a piece to split in half.
• A reputable restorer will welcome your thorough questioning before you commit your money and ceramics for restoration.

Cautions

• Severe crazing can cause the glaze to flake from the body of a ceramic object. Test its stability by gently tapping with a fingernail.
• Only peroxide – never chlorine bleach – should be used to treat stains on ceramics.
• Never glue a broken item if you intend to have in professionally restored. Leave that to the restorer.