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THE CARE AND PRESERVATION OF
Glass and Ceramics
Clara Deck, Senior Conservator, The Henry Ford
Glass and ceramic objects can be maintained for years of use
and enjoyment provided that some basic care and attention is given
to their preservation. The conservation staff at the The Henry
Ford have compiled the information in this fact sheet to help
individuals care for their objects and collections. The first
step in the care of collections is to understand and minimize
or eliminate conditions that can cause damage. The second step
is to follow basic guidelines for care, handling and cleaning.
Contents:
Causes of Damage
 Ceramics
Glass
Guidelines for Care
Handling
Display
Cleaning
Ceramics
Cleaning
Glass
Ceramic
Repair
Glass
Repair
Environment
Bibliography
Suppliers
References
CAUSES OF DAMAGE
Glass and ceramics are among the most durable antique collectibles.
Breakage is by far the most common form of damage that occurs to
both. Additional damage in the form of stains and discoloration
can be caused by improper use, display, cleaning or repair. In rare
instances, poor manufacture or harsh environmental conditions lead
to degradation.
CERAMICS
Ceramics can become permanently stained by a variety of factors
including inappropriate cleaning, repairs or careless use.
Porous, unglazed or cracked ceramics can develop stains as a result
of being soaked in water during cleaning. The absorption of colored
materials such as foodstuffs, soil from potted plants or rust
from contact with metal objects can also cause staining. In addition,
the use of inappropriate or poor quality adhesives and paints
during the restoration process can also result in irreversible
discoloration.
Antique ceramic dishes and bowls should never be heated beyond
room temperature. Elevated temperatures can cause darkening of
already existing stains and sudden changes in temperature can
promote the development of cracks.
In the case of archaeological ceramics, damage can be caused by
the presence of salts that have been absorbed into the object
from the soil in which it was buried. These salts can absorb moisture
from the air when humidity levels are high. This absorption of
moisture causes the expansion of the salts which can lead to cracking
or delamination of the ceramic object. The primary method for
preserving archaeological ceramics is to provide a stable environment.
GLASS
In rare instances, a damaging condition called "weeping glass"
occurs. "Weeping glass" manifests itself in the form
of droplets of moisture that form on the surface of a glass object.
These droplets of moisture can actually leach out unstable components
of the glass producing an alkaline solution. If these alkaline
droplets remain on the surface of the glass for a long period
of time the surface will develop a fine network of cracks. This
phenomena is referred to as "crizzling". Both crizzling
and weeping are believed to be the result of improper formulation
during glass manufacture.
Glass can also be permanently damaged by lengthy exposure to acidic
or alkaline conditions such as in the case of archaeological glass.
Glass that has been buried in the soil for long periods of time
develops a matte, scaly and "iridescent surface". In
the case of archaeological antiques, the iridescent scaly surface
has become a prized aesthetic quality that is actually desirable
for collectors of archaeological glass.
The primary method for stabilizing damaged glass is to provide
a stable environment.
GUIDELINES FOR CARE
HANDLING
The primary cause of damage to both glass and ceramic objects
is mishandling. Careless handling can result in breakage, chips
and scratches that mar the beauty of glass and ceramic antiques.
The careful handling and storage of glass and ceramic objects
is the surest way to provide protection. Always use two hands
when lifting or moving objects, being careful to lift them from
their strongest points. Never lift objects by their by handles
or spout. This is particularly important in the case of objects
that have been repaired previously. Even the best repairs can
not completely restore the structural strength to a broken glass
or ceramic item.
Whenever possible, stacked items should be cushioned using felt,
soft cloth, or polyester padding to avoid abrasion of decorative
surface elements. Care should also be taken to avoid rubbing gilded
or iridescent glass surfaces since they can be easily worn off.
DISPLAY
The use of spring-type metal plate hangers should be avoided.
These hangers place a great deal of stress on objects and can
lead to the development of cracks. Metal hangers can also scratch
the surface of the object. Plate stands constructed of hard plastic
or painted wood that allow the object to rest at a tilted angle
are preferable (these stands are available at Michael's Crafts
and Pier I Imports).
CLEANING CERAMICS
Although ceramics are generally considered to be stable materials,
a certain amount of caution must be used when cleaning them. Archaeological
and low-fired porous ceramics should only be cleaned by a trained
conservators. The majority of ceramic items however, can be successfully
cleaned provided that a few basic instruction are followed.
Some antique ceramics contain fragile painted or gilded surface
decoration which can be removed or damaged by harsh cleaning solutions.
It is important to use only dilute cleaning solutions, applied
with soft cloths during cleaning. Antique ceramics should never
be soaked in any liquid. Prolonged soaking and uneven drying can
lead to staining of ceramics. This is particularly probable in
items that are chipped, scratched or that have cracked glazes.
Lastly, automatic dishwashers should never be used to clean antique
ceramics.
Recommended materials for cleaning ceramic objects include mild
detergents in water. The detergents most commonly used here at
the Henry Ford Museum are Triton X-100, Vulpex and Orvus. All
three products are available from Conservation Resources International
L.L.C. (see Suppliers list below). A mixture of ethanol (ethyl
alcohol) and water 1:1 can also be used for cleaning.
Before proceeding to clean an object, it is important to inspect
and test the object to make sure that no elements will be removed
or damaged during cleaning. Examine the object to determine if
there is any flaking gilding or paint that could be wiped away
during cleaning. Once it has been determined that it is safe to
proceed with cleaning, the cleaning solution should be tested
in a small inconspicuous area to insure that decorative designs
will not be damaged.
Dilute detergents (approximately 1% in water) should be applied
using a soft cloth or cotton balls. The residual detergent should
be removed by rinsing with distilled water applied also with a
cloth or cotton balls. In both instances, the cloth should be
damp not wet. The object should then be allowed to air dry.
Additional cleaning involving the removal of tenacious stains
and dirt should be left to a professional conservator.
CLEANING GLASS
Glass can be cleaned in much the same manner as ceramics...with
the addition of dilute ammonia as a cleaner. "Weeping"
glass and archaeological glass should only be cleaned by a professional
conservator.
CERAMIC REPAIR
Choosing an adhesive for a ceramic object is not always a simple
task since it depends on the porosity and overall condition of
the object. A poor choice can result in irreparable staining.
As such, it is recommended that a conservator be consulted.
GLASS REPAIR
Archaeological glass, painted glass and glass photographs can
be easily damaged by inappropriate repairs and, therefore, should
be repaired only by professional conservator.
The majority of other types of glass objects can be safely repaired
in the following manner:
The most commonly used adhesive for the repair of glass objects
is epoxy. The adhesive used most often at the Henry Ford Museum
is Hxtal (available from Conservation Resources International
L.L.C. - see Supplier list below). Hxtal is a strong clear adhesive
that is relatively light stable. The major disadvantage to using
epoxies is that they discolor with time and exposure to light.
Hxtal is one of the most stable epoxies that is currently available.
Many commercially available epoxies discolor within a short period
of time resulting in unsightly repairs.
When repairing a broken glass object, care should be taken to
avoid abrading broken edges while trying to align them. Abraded
edges will prevent proper alignment during repair. Once the adhesive
has been applied to all broken edges the pieces should be aligned
and secured until the adhesive sets. Clear adhesive tape or strapping
tape works well to hold fragments together as the adhesive cures.
Residual adhesive should be removed prior to curing using acetone
that is applied with a soft rag or cotton swabs.
The adhesive should be allowed to set for at least 72 hours prior
to removal of the adhesive tape.
Once a glass object has been repaired using epoxy, it should be
kept out of direct sunlight. Sunlight will accelerate the yellowing
of the adhesive. Although epoxy is a strong adhesive it may not
withstand prolonged soaking. The object should not be soaked in
liquids as they may loosen the mended area.
ENVIRONMENT
It is preferable to store damaged and unstable antiques such as
archaeological objects and "weeping glass" in areas
where temperature and humidity levels can be controlled and monitored.
The recommended temperature and humidity levels are as follows:
| Weeping
Glass |
Temperature
Relative Humidity |
65-70
F
40% |
| Crizzling
Glass |
Temperature
Relative Humidity |
65-70
F
55% |
| Archaeological
Ceramics |
Temperature
Relative Humidity |
65-70
F
45% |
* It is critical to avoid fluctuations
While precise control of temperature and humidity is desirable,
it is not always practical in homes. Therefore, damage should
be minimized by avoiding extremes in temperature and humidity.
This can be done by insuring that objects are kept away from heat
sources such as furnace vents, fire places, warm lights, direct
sunlight, and internally lit display cases. Inexpensive temperature
and humidity indicators can be purchased from conservation suppliers.
BIBLIOGRAPHY
The National Trust Manual of Housekeeping
Sandwith and Stainton
Penguin Books Ltd.
536 Kings Rd
London SW10OUH
The Conservation and Restoration of Ceramics
Susan Buys, Victoria Oakley
Butterworth-Heinemann
London
ICC CCI Notes
Canadian Conservation Institute Notes
The Care of Ceramics and Glass 5/1
1030 Innes
Ottawa, Canada
K1A 0C8
613-998-3721
Brill,R. "Crizzling-A Problem in Glass Conservation,"
Conservation in archaeology and the applied arts. International
Institute for Conservation (1975) 121-134
Lins, P. Andrew. "Ceramic and Glass Conservation: Preventive
Measures", Museum News. 55, No. 3 (1977): 5-9
Rottenberg, Barbara Long. Care and Display of Glass Collections.
American Association for State and Local History, Technical Leaflet
127, 1980
SUPPLIERS
Conservation Resources International L.L.C.
8000-H Forbes Place
Springfield, VA 22151
1-800-634-6932
Fax: 703-321-0629
Vulpex and Orvus Detergents, Hxtal Epoxy
University Products
517 Main Street
PO Box 101
Holyoke, MA
1-800-762-1165
Humidity indicators
Hardware stores
Acetone and Ethanol (ethyl alcohol)
Michael's Crafts and Pier I Imports
Plate stands
REFERENCES
For a listing of conservators in your area, please contact:
The American Institute for Conservation of Historic & Artistic
Works
1717 K Street NW
Suite 301
Washington, DC 20006
(202) 452-9545
http://aic.stanford.edu/guide/form.html
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