# Pyrex vs. Corning ware



## wywiwyg2000 (Mar 6, 2012)

A newbie mistake.
I thought a Pyrex baking dish is the same as a casserole dish. My Pyrex dish broke after being warmed on my hot plate. I started the temperature low and then slowly increased. I was going to boil the Nitric acid from my cementing process. Should I use only Corning ware to put on a hotplate? Also, does the Pyrex flasks, work with the hotplate? I was using this process instead of the flame.


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## maynman1751 (Mar 6, 2012)

Was there any liquid in the vessel? I believe that you MUST have something in it to avoid hot spots. If you're using a coil type, try putting a sheet of steel between the hotplate and the vessel. It will help distribute the heat more evenly.
DON"T BOIL! Heat to evaporate at just under boiling temp.


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## element47 (Mar 6, 2012)

I am NOT speaking from experience here, but my impression is that an old Pyrex dish is likely to have scratches in it which can cause failures, fractures. And, a hotplate, depending upon the exact nature of the top surface (flat metal, or, coiled up heating wire within ceramic grooves on a "waffle" shaped top element) these things can create micro scratches and create failures where you would think they wouldn't. But they apparently do. ...I have been surprised at the numbers of failures I have read about from users. I believe the preferred method is to place some fine sand atop the hot plate which seems to act as a buffer and to prevent localized hot spots.


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## nickvc (Mar 6, 2012)

Both good factual replies, the moral is never put glassware, even lab glass, onto an element directly they will fail, your lucky if you lost no values..


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## butcher (Mar 6, 2012)

From my understanding there are older and newer corning ware casserole dishes, with the older dishes being better about not breaking on a hot plate, I have had good luck with the white corning casserole dish, on a hot plate, with care not heating up or cooling too fast have never had one break, I even heat them to high and incinerate powders in them with a propane torch.

Important my hot plate burners are solid cast iron type burners, not the spiral coil type, this helps heat to distribute evenly and not create hot spots.

(If using a coil type burner you maybe try a wire screen between dish and burner, or a piece of solid steel plate), 

(Test the corning dish before using it by boiling water, also by heating empty, and also heating dirt and using propane torch on corning ware dish with high heat, give it a good work out, wear safety glasses, if you can abuse it and not break it, then you should be able to trust its use with care, do not do this with Pyrex or lab glass).

Also the amber (yellowish brown), or the violet Pyrex stove top glass type skillets, I also have good luck with (these are not the same as a Pyrex baking dish, i would not use those), (you can test these as above)..

Pyrex glass coffee pots from a automatic coffee maker will hold up fairly well on the solid hot plate burner, (see sitting it in corning cassarole dish below).
But care is needed they will break if powders are heated in settled bottom of solution strongly (uneven heating), or if temperature is changed rapidly, or if the burner does not heat them evenly (I use solid burner hotplate, do not change temperature fast and if heating powders in bottom of solution keep them stirred).

I have not used lab glass Pyrex, but I suspect it is similar to the coffee pot above, and same care would apply.

Also pyrex is a brand name so all pyrex glass is not the same, do not heat thick pyrex glass on a stove top burner unless it is made for stove top.
A catch pan under your hotplate incase of breakage.

Some heat the automatic coffee pot sitting in a white corning dish (corning dish acting as catch basin and spreading heat evenly to glass pot), sometimes I do this, but most of the time I will use the corning dish directly, incinerating and dissolving solutions in the dish, I can almost do a whole process without moving the dish from the burner or without moving the metal or powders from the dish (only removing dissolved metals in solution when needed with suction bulb tool).


There was another long discussion on this topic search the forum (use Laser Steve's web site for the search) type in casserole dish, or heating glass, or hotplate burner).


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## publius (Mar 6, 2012)

hotspots will cause glassware to crack. An electric hot plate or a gas flame may cause stress fractures. My experience is that it is best to place that type of glassware on a bed of sand. The sand need not be very thick. 1/4 to 1/2 inch thickness should allow intimate contact with your glassware preventing cracking. Just my 0.02 USD


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## goldsilverpro (Mar 6, 2012)

When I have values in a container that is placed on direct heat, such as a hotplate, I want to be guaranteed that the container won't break. In 46 years I have only found 2 kitchen products, both made by Corning Ware, that meet this requirement. Everything else I've tried broke on the heat. 

(1) Vision ware. 
http://www.ebay.com/sch/i.html?_nkw=vision+ware&_armrs=1&_from=&_ipg=

(2) Corning Ware pyroceram dishes. The trademark for the newer ones is StoveTop. The only ones I have used are shaped like this. Some new ones are plain white (1st link) and some have a pattern on them (2nd link). I have tried other types of white Corning Ware dishes and they all broke.
http://www.shopworldkitchen.com/corningware/stovetop-just-white-casserole-jw-5c-b
http://www.shopworldkitchen.com/corningware/stovetop-blue-cornflower-casserole-bf-5c-b

Older pyroceram dishes of this same square shape are available on eBay and flea markets. Every older one I have seen (all square) has a pattern on it. Some pattern names are Blue Cornflower, Wildflower, Spice of Life, Symphony, and Abundance. Here's some listings on eBay. I would not buy a used one unless it was in perfect condition - no chips, no cracks. The glaze on the inside should be flawlessly smooth.
http://www.ebay.com/sch/i.html?_ipg=&_from=&_armrs=1&_kw=corning+ware+5+quart

I have used these for dissolving, evaporation, drying gold, etc. When I heat a beaker, I most always place it in one of these dishes and put the dish on the hotplate.


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## wywiwyg2000 (Mar 6, 2012)

Thank you for all the excellent information. Luckily I had the hotplate and solution in a big oil drain tub, no loss but the baking dish. The Pyrex pitcher just stayed in place with a broken piece under it. I am not sure about my hotplate. The top looks and feels like a hard durometer rubber, but it is black metal that looks like an old phonograph record. I have seen pictures with the sand under the vessel. I will probably try the sheet metal, since I am a long way from the beach. I will search for the old corning ware dishes you described. One more question. Will a cast iron skillet work in place of the sheet metal.

Thanks again,
Gene


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## butcher (Mar 7, 2012)

Go to second hand store and look for the corning ware casserole dish, it would work better than a cast iron skillet, you can put a piece of heavy screen wire between hot plate and corning ware casserole dish, then set your lab glass vessel in corning ware casserole dish, do not heat the lab ware strongly if powder are settled in bottom the glass will be hotter at bottom and break.

It also sounds like your hot plate is the solid cast iron burner type like I use with a black coating.


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## zuberb (Mar 9, 2012)

I wish I had seen this post before today. I purchased a Corningware baking dish today and I just attempted to use it on my hotplate to evaporate my battery acid. Like the first post said, I kept the heat low starting out and the dish cracked right down the middle before I even got to level 4. I''ve moved my 1000ml beaker over to the second (smaller) hot plate, and I'm currently using dry sweep as a buffer. Doesn't seem to be conducting heat very well, but at level 7 it's starting to show evaporation on the sides of the beaker. I'm not rushing it. I'll just let it evaporate slowly. Meanwhile, I'll be watching the second-hand stores for the casserole, or one of the Visionware things. Live and learn I guess. Luckily it was only $19, but still...


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## Geo (Mar 10, 2012)

i believe in the power of the pyroceram dishes, but the only one ive been able to find was confiscated by my wife as it had the lid with it. :roll: i am currently still using my large cast iron skillets. i have a deep #12 and a shallow #12 and a standard #14 and a 5Q cast iron dutch oven. these will have to do until i can sneak past the little woman.


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## wywiwyg2000 (Mar 10, 2012)

The older Corning Ware that came back is the good dish. Look at the links to Corningware on "goldsilverpro". This shows the new pyroceram dishes. They might be a little high, but now I see that they are well worth the money.
Thanks again. I used the sand and plate under my pot. No breaks. Thanks.


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