Wednesday, March 25, 2009

QUESTION AND TIP ABOUT GLASS

From an email from L.T.:
I recently put a vintage glass rectangular refrigerator dish in the microwave. The dish had the typical ribbed base and embossed fruit on the lid. Within no time, the lid cracked into three pieces. I thought all glass was safe in a microwave. Did this dish have a hairline I didn't notice or will this happen to all refrigerator dishes of this age and style?


Tip (and an answer to L.T.'s question):
Terry:
I can answer because I did the same thing to a glass dish with embossed fruit. I have no proof, but I think the difference between the thickness of the glass in the raised fruit and the surrounding dish caused a stress point. I have used plain ribbed glass storage dishes in the microwave often, with no trouble. Glass should be OK, in general, but I wouldn't try cut glass, either. It would break on a deep cut. One of my pieces did when I put a bowl of hot liquid Jell-O in the refrigerator to cool. The change in temperature did the damage. Glass "ages." It becomes more brittle as it gets older. That's why you must check glass shelves. They bend slightly and eventually break if they're holding heavy objects.




15 comments:

E.L. said...

Oh, do you have my attention!! Have Grandmothers oak, bowed front, lions head, claw feet, mirrowed back china cabinet....
with glass shelves..5/16 to 3/8" thick. Immediately checked them and can't see any bowing. China is all on bottom oak shelf so glassware and silver are on the glass ones. Do I have a cause to worry?
Have depression glass but never tried it in the microwave, now certainly will not. THANKS for the tip and sorry yours broke!
E.L.

EditorMule said...

I'd heard that older glass contained lead or some other substance which would cause it to crack in microwave. Anyone else ever heard anything similar? I know about lead crystal but didn't know if this would apply to glass or Pyrex items.
-VM

Anonymous said...

In reference to the refrigerator dish in the microwave....my rule of thumb is ALWAYS, don't put into the dishwasher or microwave unless it states it is safe to do so. This goes for any vintage kitchenware. Wooden handles will dry out a crack, bakelight will discolor and can crack not to mention get a white film developing on it. Any glass or china objects dating before 1970 should never ever go into the microwave or dishwasher. It may take more time to wash by hand but it is worth it.

Anonymous said...

Care must also be taken in moving glass from hot to cold/cold to hot environments such as when traveling or shipping during certain seasons. Sudden temperature changes can be disastrous. Vintage glass can be quite fragile. Never display in direct sunlight, etc. K.B.

Anonymous said...

I haven't had the experience of putting a 'vintage' glass piece in a microwave, however-think about it-the term 'vintage'. Don't think they had microwaves then. I would suggest that any glass items older than about 30 yrs. not be subjected to microwaving.

Anonymous said...

Never put vintage glass/pottery/ceramic/porcelain/etckitchenware in the microwave! These items were not made to withstand the microwaves which cause the heating. Only use items modern kitchenware marked microwavable. Also never nuke anything with metal on it, ie: gold/silver trimming.

MAM

Happy said...

I think that maybe it's the make up of the glass. I had the same thing happen with a creamer, that I was heating syrup in. Could it be the lead content? I say don't use antique glass in the microwave.

Anonymous said...

I GUESS THAT THOSE GLASS REFRIGERATOR DISHES WITH THE EMBOSSED FRUIT DESIGN DON'T MIX WITH MICROWAVES. MANY YRS AGO WHEN MY MOM GOT HER FIRST MICROWAVE - MUST HV BN THE LATE
70'S - THE SAME THING HAPPENED TO HERS. IT SPLIT INTO TWO PCS.

Cliff Oswald said...

As a person who has often had the opportunity to work with old glass (I'm stained glass restorer) I'd like to put everyone's mind at ease; pardon the correction Terry, but glass does not get brittle with age.

Glass found in Roman ruins showed a marked thickening at the bottom and a corresponding thinness at the top.

Glass is actually a liquid. 'frozen' at our normal room temperatures.

Those of you with old glass shelves in cabinets are safe as long as the shelf is in good condition, with nothing more than very mild surface scratches. Any chipping on the edges of the glass should be wet-sanded to smoothen off any sharp edges, as these can lead to glass breaking under load.
If there are metal clips supporting the shelves, felt pads are good, to ensure there are no pointy spots that will induce an uneven stress.
As for pressed and cut glass pieces, the difference in thicknesses will cause the glass to heat unevenly. Terry's advice on not using them in a microwave will be heeded in our kitchen from now on. Thanks Terry.

Anonymous said...

Microwave ovens came into common use in the early 1970s.If your piece of pottery or glass was made before that date, do not use it in the microwave-or the dishwasher; unless you're brave or don't care about that item that you inherited, or scoured every garage sale or flea market to find.

Anonymous said...

Sadly, I did the same thing with a "vintage" (my age!) refrigerator dish as described with the same results. Should have known better about microwaving or using in the dishwasher anything that's vintage like me! We all learn eventually! Thanks for all the info & tips on this site. M.B.

Anonymous said...

much older glass ( and perhaps some glass "now days")does have lead and perhaps other more solid minerals/substances that do not move around molecule wise in microwave....ie...thats why we dont put metal pans etc...in microwave....

Anonymous said...

I believe the glass must be 'tempered' for microwave cooking. Most 'post microwave oven' glass AND PLASTIC wear (learned that the hard way as well!) will be 'iffy' when used in the microwave.

S said...

All glass expands and contracts as it heats and as it cools. This is called the coefficient of expansion, and different types of glass have different COE's. The lid to the refrigerator dish with it's embossed design had a variety of thicknesses and when it heated, it heated unevenly, causing some portions to expand more quickly than others, and this may have caused the lid to crack.

Cindy Coldiron said...

Hi:

I just wanted to add my two cents about glass as well. I am a glass artist and work with kiln-formed glass at high temperatures.

I would never put any piece of glass in the microwave since the heat up is too quick and the cool down will be as well. All glass, regardless of thickness, will be prone to crack in those circumstances.

If I heat up or cool down a piece too quickly in the kiln, I will get a huge stress crack or break.

Hope this helps.

Cindy

Arlington, VA