“Sick” Glass and Its Problems

Cut-glass decanters, colognes, water bottles, and the like often have dirty or stained interiors that detract from their overall appearance. When surficial dirt — which is not the “sickness” that is discussed in this file — is the culprit, a simple cleaning may be all this is necessary. Mild detergent and/or a dental cleanser can be used and they are perfectly safe. Adding uncooked rice or peas and swishing the mixture around can accelerate the cleaning action. The item should be thoroughly rinsed, drained and dried. One should take extra case that the interior has been dried completely, especially if a stopper is to be replaced. Strips of paper toweling, with the assistance of a wooden dowel, can be used to speed the drying process; hair dryers probably should be avoided. Also, one should avoid using any scouring agent that is harder than the glass itself (for example, buckshot!). A word of caution concerning toilet cleaners: A dealer known to the writer once used such an agent in a decanter, and the decanter exploded, fortunately causing embarrassment rather than any physical harm.

It is always good practice to observe the interior of any cut-glass container — or, for that matter, any cut glass — in bright sunshine, or at least under the direct beam of a strong indoor light source, before purchasing the item. Be sure that the interior is completely dry, and that it has not been “waxed” or “oiled” — methods used by dishonest sellers to mask stains. Never buy a container that has even a small amount of condensation on the surface of its interior.

Sometimes the cleaning procedure described here will not remove stains completely — the glass will continue to appear dirty. Such glass is commonly described as “sick,” a general term used by dealers and collectors that includes defects that are either curable or incurable. 

                  Curable “Sick” Glass

This category includes items that have been stained by hard water or have had their interior surfaces degraded by oxidation, a process enhanced by the presence of liquids such as wine and vinegar. These stains, which are readily visible, may be white or bluish-white. This discoloration occurs because liquids have been stored in the containers. Fortunately these stained surfaces — even when etched by a weak acidic solution — can usually be polished and thereby restored to their original condition. One of two methods is used: either mechanical (abrasive) or chemical (acid). The former uses brushes and a polishing agent such as cerium oxide, the latter an acid solution (note 1). In the writer’s experience, the former method is preferred but it may not be available or appropriate. Either method is best left to professionals. The owner of such “sick” glass should not undertake any treatment that is harsher than the cleaning methods described above.

At one time a glass restorer in Connecticut carried the polishing of “sick” glass to an extreme degree by dipping the entire item into a vat of acid. Fine, wood-polished pieces were ruined by this treatment because both exterior surfaces, as well as interior surfaces, were “polished.” Although he is no longer in business, one can probably find examples of his technique today. Several of this country’s “important” dealers used his services. (This is another reason for the buyer to learn to tell the difference between mechanical and chemical polishing.)

The writer does not often purchase stained glass for re-sale because it is difficult to sell even a slightly stained item in today’s marketplace. And the outcome of any polishing technique cannot be guaranteed. If the reader insists on buying a “sick” piece of cut glass that is curable, a cost estimate should first be obtained from the restorer. If he or she is legitimate, the inquirer will be told whether a mechnical or a chemical process will be used. Details of whichever process is used may legitimately involve trade secrets, however, and they should be respected. The restorer should be able to supply references, and they should be consulted before sending off any item to be polished. It is sometimes worthwhile having a small, inexpensive item treated as a “trial,” although this will not necessarily be a predictor for future items. It should also be noted that some restorers will only work on items that are round or oval in cross-section — square decanters can be a problem.

                   Incurable “Sick” Glass (Crizzling)

The following information appeared in an article by Stephen P. Koob that was published in The Corning Museum of Glass, Annual Report 1999, p. 22:

Crizzling usually occurs in 16th — 19th-century European, American and East Asian glasses. The durability of these objects is endangered by an excess of alkali (soda, potash, or a mixture of these two compounds) in the glass and/or a deficiency in stabilizers, the most common of which is lime. [Lead oxide is also a stabilizaer.] As water is attracted to the surface of the glass, the excess alkali is leached out, eventually resulting in an attack on the silica in the glass. The first signs of crizzling may be a slightly hazy or cloudy appearance to the glass. In time, fine cracks develop. This cracking, which worsens in very dry conditions, is irreversible. At last, the glass breaks apart.

As far as we know, crizzling cannot be completely stopped or prevented. The best we can hope for is to slow the process to a virtual standstill. Our new [display] cases seal well, which provides for a very stable environment, even if the outside air changes. On the bottom of each case is a large tray in which silica gel (a common desiccant that can be “conditioned” to maintain a set moisture environment in a closed space) is placed as needed.

Approximately 300 objects [in the collection owned by the Corning Museum of Glass] have been identified as crizzled (about one percent of the Corning collection). Most of these pieces are now on display in the Study Gallery, but the very seriously crizzled objects are in storage in containers with silica gel.

Crizzled glass, which is also called scissle or crackle glass, is difficult to detect in its earliest stage. As with any glass, the item should be observed in bright sunshine or in the beam of a strong light. When inspecting glass for crizzling, tilt the object in various directions under the light source. If this defect is present, a sparkling network of fine lines — which are actually the tiny cracks mentioned by Koob — will appear in the glass. They look somewhat like a spider’s web. Because such glass would have been discarded at the time it was made — and not finished with cutting or engraving — it is obvious that crizzling is a progressive “disease.” It is said that Queen Mary, during her lifetime, observed the slow deterioration of some of the items in the British royal collection of antique glassware.

The writer has found several examples of crizzled glass in collections of American Brilliant Period cut glass over the years. Its presence is not rare, unfortunately. In one instance the deterioration — of a trumpet vase cut in Hawkes’ Navarre pattern — had progressed to such an extent that the entire vessel was opaque! This case was exceptional. More usually the crizzling, when found, is not obvious at first glance; it therefore pays to look specifically for this defect. At the present time the writer has a tumbler made by C. Dorflinger & Sons that has “early stage crizzling” and he has also had finger bowls cut by Hawkes in the expensive Kensington pattern that were similarly afflicted.

It is surprising to find examples of diseased glassware today, considering that it was made at a time when the manufacture of fine glass was scientifically controlled. Nevertheless, crizzled glass appears often enough to be a matter of some concern.


1. Matthews, Thomas, 1994: Mysteries of sick glass, The Hobstar, Vol. 16, No. 5, pp. 1, 5 (Jan).