Crossposted at Politicook.net, and kick my butt if I do not begin that way ever again.
This diary will be a little shorter than usual and I can only stay around for an hour or so because I am leaving at the crack of dawn to drive to Arkansas. Tonight we are going to discuss glass cookware.
Included in this definition also are ceramics, porcelain-covered materials, stoneware, and earthenware, since they are all based on silicates. There are probably more kinds of glass than any other commonly manufactured substance, and properties can be tailored to suit different needs.
In the kitchen, the most common kind of glass is soda-lime glass, the cheapest and most common type. Made from sand, sodium carbonate, and lime, all cheap materials, it is used in windows, bottles, canning jars, and drinking glasses. Like most glass, it is brittle and shatters easily from mechanical shock. It is also subject to breakage from thermal shock, so it is not very useful for stovetop or oven use.
A much better material for cooking use is borosilicate glass, the so called Pyrex. It is made of sand and borax, with very little lime and a little aluminum. The advantage of Pyrex that is has a much better resistance to thermal shock that soda lime glass, so makes much better cookware. It is also less soluble than soda lime glass, and so is less likely to etch when used with basic foodstuffs. It is not immune, however, so pouring cold water into a hot pan is not recommended.
Almost all bake ware that is clear is Pyrex, whether or not it says so on it. A variation is Visions, which is technically not a glass, but a glass-ceramic. (CorningWare is also a glass-ceramic. I suppose that I should explain the difference.
A glass is a material that, when solidified, has no identifiable crystal structure. A ceramic does have identifiable crystals, although they may be small. Due to the fact that the crystals are large enough to scatter light, ceramics are not in general transparent. Glass ceramic materials have crystals embedded in a glass matrix. In Visions, the crystals are small enough not to scatter light, but in CorningWare they are. This composite structure offers advantages in both strength and thermal shock resistance.
Another composite is Corelle. It is interesting because it consists of three layers: a central core of a glass-ceramic and outer layers of a strong glass. Some of the specific information seems to be proprietary, but it seems that Corelle is also tempered. It is one of the lightest glass materials in the kitchen and is safe for microwave and oven, but no stovetop or broiling. When it is dropped, it tends to fail catastrophically by explosion, characteristic of tempered glass materials.
Ceramic coated metal cookware is common, and are fine for roasting. Because they are thin, they are not so good for stovetop use except for very watery materials, since they are prone to stick with thicker materials. Interestingly, the ceramic material coating the metal has exactly the same coefficient of thermal expansion as the metal, or otherwise the ceramic would flake off the first time it was heated.
Earthenware (also called stoneware) is made from clay which is shaped (either on a wheel, or for mass production, in molds) and fired in an oven. A glaze is added and the pieces refired, or in some processes the glaze is added before firing. The center of the material is a crystalline ceramic, and the surface is a glass. This is important, because it is porous and would absorb water and other materials without the glassy glaze. Most stoneware is OK for oven and microwave use, but not for broiling or stovetop.
China is a ceramic of higher quality, and thus greate expense, than earthenware. It is made of more carefully selected and purified clay, and is generally fired at a higher temperature. China is translucent to light, whilst earthenware is not. It is more glasslike than earthenware, but still a ceramic. China is generally glazed, but is not nearly as porous as earthenware.
Unglazed earthenware is sometimes seen, the most familiar kitchen device being a "stone" bread oven board. Some people use large earthenware planting pots to make impromptu outdoor ovens, but that is not really cookware.
I only have a few cautions for you about glass and ceramics objects. All of them will break if sufficiently impacted or thermally shocked, and some are tougher than others. Enamalware metal objects will chip if impacted, then rusting is likely. In addition, if the chip is in the food contact zone, the metal may react with the food being cooked as discussed last week.
Some cheap imported earthenware, especially from Mexico and China, is glazed with materials extremely high in lead. This lead is fairly easily leached into foods, especially acidic foods. There have been documented cases of lead poisoning from storing orange juice in these pitchers, so if you have Mexican or Chinese earthenware, be cautious using it.
All in all, vitreous cookware wears well and is unexcelled for many purposes, especially oven and microwave use. As always, any comments, questions, or other science topics are welcome. As I said, I am leaving early tomorrow morning, so will have to limit my responses to an hour tonight.
UPDATE: Folks, thank you for the comments, questions, and kind thoughts. I stayed half an hour later than I had planned, but I must get ready for the trip tomorrow. Clothes are already in the car, and suitcase is ready except for the shaving kit that I will use tomorrow morning. I have frozen stuff from the garden that will go into the cooler tomorrow morning, and canned stuff from the garden that I fear to load tonight because it is going to freeze here tonight. 620 miles to go tomorrow, but Interstate almost all of the way. I am blessed with the ability to stop only when fuel is needed (if you get my drift), so I can make the trip in 10 hours if nothing bad happens. A 62 MPH average is not bad, and I do not speed.
I will try to respond to any other comments that I miss tonight if I get to Arkansas before the diary is closed to them.
UPDATE the Second: I will leave this open and check in from time to time as I work towards getting ready to go. If you do not get a prompt reply from me, it is because I am doing other things and will check only every half hour or so. Those of you who read my posts know that I am not a "hit and run" diarist.
UPDATE the Final: Thanks for putting up with my slow responses to you. I loaded the car with everything except the frozen food and the computer since it is not going to freeze tonight. Clock is set for dark:30, and Mrs. Translator has agreed to call to make sure that I am awake and ready to load the frozen food into the cooler and pack it with below zero F bottles of frozen water. Tomorrow, a quick shower, pack the shaving kit into the suitcase, and finish loading the vehicle. A quick stop at the store to pick up some more sweet potatoes at a quarter a pound, and I am on the way. Everyone here, please have a wonderful Thanksgiving and hug and kiss your loved ones. I am more optimistic now than in years, because I am going to list myself in the Kossack Employment database Tuesday. I know that I will get work! I would have done it sooner, but getting ready to bring all of this stuff (much of which is not noted) to the family took a lot of time.
Happy Thanksgiving to everyone, and I will try to check in tomorrow night to respond to questions. All, be careful out there!
Warmest regards,
Doc