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Damage & Defects

You may have seen books on Pyrex collecting which give suggested values of various pieces. It's important to note that such values are only applicable to pieces in excellent condition. Collectible glass kitchenware is not regarded as having intrinsic value. That is to say, for example, a rare promotional casserole in its original box and in perfect condition may be considered to be worth several hundreds or even thousands of dollars. Not always so, however, if it is incomplete, scratched, chipped, or otherwise damaged. Just because it is what it is doesn't necessarily determine its collectible value.

While changing market conditions over the years may have affected prevailing prices, collectors continually strive to obtain the best examples of pieces as free as possible from unreasonable damage or material defects that they can. The following addresses what you should look for when assessing the value of collectible vintage Pyrex ware.


There are a few ways a piece of Pyrex or other kitchen glassware can be damaged: chipping, scratching, and chemical erosion of the finish. Unfortunately, all of them tend to be from regular usage occuring long before reaching the collectibles marketplace.

Spotting a chip is usually easy, as they are found primarily on the lip of a dish or bowl, or, if the bowl has one, the foot ring. Sometimes, what appears to be a chip is actually a void caused by an air bubble trapped in the glass as it cooled and hardened. Chips on clear glass pieces like lids are usually more easily felt than seen, so running a fingertip gently around the edges and rims is often the best way to disclose them.

Scratching is usually quite evident, especially on color finishes and on clear glass, less so on plain opal glass. Scratches from utensils in the bottoms of bowls are to be expected to some degree, and tend not to devalue a piece as much as would similar damage to an outer, colored surface. Very dark finishes such as charcoal or the deep brown fade on the Old Orchard pattern tend to show scratches more obviously than most.

Additionally, cosmetic damage can be the result of washing in an automatic dishwasher. Before environmental pollution concerns forced their removal, significant amounts of phosphates were originally contained in dishwasher detergents in order to improve their cleaning efficiency. Unfortunately, the chemical was also responsible for a variety of detrimental effects on Pyrex colorware.

Dishwasher damage, "DWD" in collector shorthand, is most often seen in that rough, faded and hazy appearance of many color ware pieces. The damage may also manifest itself as a shift in color of the decoration, so don't be quick to accept that a piece advertised as a rare color version is legitimate.

Another form of damage, stripping, may not be evident at first glance. Stripping goes beyond DWD in that the color and decoration are completely gone. Occasionally, you will see pieces advertised as being a rare plain white. Some plain opal Pyrex was indeed made in very limited instances, and not for very long in each case. More likely is that the piece has had its color removed by a previous owner, perhaps as a remedy to salvage a piece with an already damaged finish. There will often be a remnant of the original color in a crevice or at an edge.

Oddly, pieces with decoration are sometimes seen stripped of their base color via dishwasher damage, but with the applied decoration left largely intact. Or the erosion may also have removed the applied decoration, but left the base color under it largely intact. Beware of such pieces being advertised as rare or one of a kind.

Collector interest in such pieces is virtually nil. Even today, dishwasher cleaning is still inadvisable.


Although the level of quality control was apparently quite high, there are sometimes seen instances where defects slipped through. At the time, some common minor defects may have been of no concern to either manufacturer or consumer. After all, the collectibles of today were inexpensive consumer commodities when originally produced.

Most often seen are flow marks. In the process of manufacturing pressed glass articles, a blob of molten glass is cut from a larger mass and deposited into a bottom mold, and a press with the top mold lowers and spreads it out to conform to the cavity between the mold halves. Depending on certain circumstances, sometimes wavy lines are seen, most often in areas like the flat bottoms of opal glass baking pans and dishes, and in flat-topped clear glass lids. In both cases, it doesn't seem to materially impact collector interest or value. In sales literature, Corning explained that the temperature differential between the molten glass and the metal cutters was responsible for the phenomenon, and assured customers durability was not impacted. It is less-frequently seen in clear glass dishes, where it may have been more objectionable to the consumer, and thus more likely to have been rejected at time of production.

Multi-color decoration presented a special challenge in manufacture. The colored patterns were applied via a screen printing process capable of only one color at a time. A second or third color required a separate pass across a different screen. It was therefore imperative that pieces were precisely positioned by the equipment for those subsequent applications to be "in register" with the first. Most times, the process resulted in finished pieces within manufacturing tolerances, but sometimes they are seen just a little bit "off". Unless excessive enough to be a distraction, minor screen printing offsets don't seem to be a problem for most collectors.


Occasionally, you'll see variation in the distinctiveness of embossed markings, most likely the result of molding equipment wear or maintenance issues. Since this is confined to backstamps and mold numbers, this is not really considered a defect, nor does it impact value.

Decorative designs applied as a contiguous band around bowls will normally have a break of up to about an inch, depending on the size of the bowl. This is due to a limitation of the automatic handling equipment's ability to rotate the piece through a complete 360 degree circle. And perhaps it's better that way, as any mismatch or overlap of the ends would certainly be distracting.

When subjected to a backlight test, most painted bowls will exhibit an uneveness of color, with blotchy areas more opaque (or less translucent) than the rest. This phenomenon is the result of limitations in the automated application of the finish and should not be considered a defect.

Bowls which are painted decoration over plain opal glass normally exhibit varying degrees of uneveness in surface texture of the glass seen in the unpainted areas, including parts that are more or less glossy, or that may even appear superficially striated. These are artifacts of machine-pressed molding, and do not represent a defect.

Since the application of decorative patterns was a machine process, you will sometimes see what appear to be scratches running through the decorated area. If the paint itself is not scratched, what actually happened was the decoration was applied over a flow mark. While the preference of more particular collectors would be against such pieces, it really does not constitute a defect.

Flashing is what occurs when the halves of a mold do not come together as precisely as they should. When the glass is poured and pressed, some seeps out from the tiny crack between the halves, leaving a thin fin protruding from the edge of the piece. The majority is fired off as a part of the finishing process, but some is often seen (or felt) remaining on the edges of a lid or a dish handle. Typically minor, flashing does not seem to affect collectible value.

Lids do not always fit absolutely flush on dishes. No intended use required that they did. Manufacturing tolerances were not such that they were rejected if they did not. There may even be instances in which a lid will rock slightly when placed atop its dish. If otherwise undamaged, whether or not it detracts from value varies from collector to collector.

Most bowls have foot rings, and in which there are occasionally seen one or more small, shallow, smooth-edged divots. These also appear to be artifacts of the molding process, and are not detrimental to collectible value.

In Summary

Every collector and their reasons for collecting are different. Condition will matter more to some than it will to others. While minor wear or scratches may not materially affect displayability or usefulness, when subjected to close inspection they do tend to detract from collectible value.