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I currently rent, and the only problem I have with the house we're in is that it has a glass-top range. I absolutely love my cast iron cookware, and use it as often as possible.

I've heard a few reasons not to use cast iron on glass, including:

  1. You can scratch the glass if you're not careful
  2. It's very easy to break the glass if you drop it
  3. You can melt the glass top (mentioned in linked thread)
  4. It can be hard to minimize hot spots

I'm not very concerned about (1) and (2), as I've already been using cast iron on glass for years with no problems (I'm very careful when I do use it).

While researching (4) I came across (3), something I had never heard before. So, I now have a few questions:

  1. Is melting the glass really plausible? This seems unlikely to me, as a quick search revealed that lowest melting point for common glass types is 1500C or higher, a temperature I have no plans to reach - but I'm not a physicist or a chemist, nor do I know what kind of glass is used to make a glass top stove.

  2. Is a heat diffuser effective on a glass range? I have experienced a few hot spots on my large (12") skillet, and obviously when experimenting with my two-burner griddle. Would a heat diffuser help, especially with the two-burner (which I've all but given up with on glass for now because it's so uneven).

  3. Any suggestions for safely and effectively using cast iron on a glass-top range (short of being very, very careful when moving the pans)?

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I couldn't decide whether this should be one question or multiple, but because they're all related I grouped them as one. Please let me know if I should have split them up! –  stephennmcdonald Aug 10 '10 at 4:31
    
They're all very closely related, there's no reason to have split them up. Good questions! –  hobodave Aug 10 '10 at 4:51
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8 Answers 8

up vote 7 down vote accepted

I also have a glass-top stove at home. So far, I really like it: the heat is very even and there is good heat transfer, provided the pan makes good contact with the surface (one skillet I have has a bit of a lip, which makes it heat more slowly).

I've slapped skillets and pots full of water around on mine, and have yet to break it. I'm probably more careful than I would be on a metal range, but it seems sturdy.

But to your points:

1) There is no way cast iron could melt the glass. Iron melts lower than does glass (1200*C vs. 1500*C), so before you manage to melt your stove, your pan will be a puddle. It may, however, be possible to deform the stove top if you let an empty pan heat for some time. I don't see why this would be more of an issue with cast iron than with any other piece of cookware.

2) A heat defuser will work fine. Don't get the kind that is designed for use with gas, but anything else should work fine.

3) The burners on my stove are smaller than my skillet, so I find I need to move the skillet around to heat the edges. Also, flat-bottomed pans and pots seem to be much more effective on the flat glass top, as conduction seems more effective than radiation here. I polish the bottoms of my pots to get better heat transfer, although this is just me being anal.

Also: cast iron can't scratch glass. Glass is much harder than iron (see this wikipedia article), glass having a 6-7 on the Mohs scale, iron having a 4.

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Cast iron is not pure iron, it's an alloy, with other metals added to increase hardness. It can definitely scratch a glass cooktop if you're not careful with it. –  ceejayoz Aug 10 '10 at 13:36
    
It is true that cast iron is harder than iron, but I can't find any measurements of hardness. It can apparently vary significantly--I imagine cookware would be made from softer (less brittle) alloy. The hardness of glass can also vary: new iPhones have a very hard glass that is extremely difficult to scratch. I've never managed to scratch my glass, with extensive use. It probably would require some sort of sharp edge, if it is possible. –  Adam Shiemke Aug 10 '10 at 15:15
    
I saw a video of someone actively trying to scratch their Droid with a set of keys to no avail. I wonder how the hardness of a glass range compares to the new smartphone glass. Either way, I'll play it safe and not hulk smash...plus, lifting a 12" cast iron skillet to shake it gives me a nice mini working. –  stephennmcdonald Aug 11 '10 at 1:43
    
I think dirt/dust is the key to scratching glass. I've too taken very sharp objects to an old iPod Touch (1st gen) screen and could not scratch it. But my iPhone 5 has some very small scratches and I am very careful with it. –  Chris Wagner May 18 '13 at 17:59
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Regarding (3) melting glass top:

  • I have, unfortunately, successfully melted a glass top range to a piece of cookware.

However, it was not with cast iron; it was with a powder-coated iron teapot. I sat down to boil some water, walked away, and forgot about it. The teapot spout did not sound, and the water boiled out of the pot. It sat on there probably 30 minutes without my attendance. When I finally remembered, I turned off the burner and tried to remove the teapot. The teapot had fused its powder-coated ceramic layer to the rangetop. When I removed the teapot, a piece of the rangetop came with it. It was a piece of about 0.5" diameter.

Based on my experience with this, I doubt a cast iron would fuse to the rangetop. It's the glass-like coating that may fuse (but not melt)

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Wow...great anecdote, I never considered that a pan's coating might fuse to a glass range under any circumstances. +1! –  stephennmcdonald Aug 11 '10 at 1:46
    
I found this thread, because my new range's manual suggests not using cast iron. It specifically mentions porcelain enamel might 'melt' onto the surface. –  MADCookie Mar 30 '12 at 15:56
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The idea that cast iron can somehow melt the glass range is just wrong. The cast iron can't get any hotter than the range surface itself can get. If the cast iron could melt the glass, then that means the range could melt itself.

I've only used a glass range at friend's houses, but they didn't seem particularly fragile. As long as you aren't hulk smashing your pans into the glass, it's pretty hard to break.

I have no experience with heat diffusers.

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If it's an induction range, you can get the pan hotter than the range surface. I have no idea if that applies in stephen's case. My guess is that any surface meant to have pans heated on it would be able to handle any reasonable temperature range that would arise from using them. –  Tim Gilbert Aug 10 '10 at 5:05
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If it's an induction range, you would need special pans. Cast iron wouldn't work. Ergo, not induction. –  daniel Aug 10 '10 at 5:09
    
@Tim: Sort of true. While the surface isn't heating the pan, the pan is still heating the surface, when in use the difference in temperature would be negligible I'd imagine. No? @roux: Are you sure? I was under the impression that anything magnetic works with induction, and that cast iron is specifically good for induction. –  hobodave Aug 10 '10 at 5:15
    
Wow - you guys are fast, even this late at night! This is just a normal glass-top range, no induction here. So far I've managed not to hulk smash anything - but now that I have that hilarious picture in my head, it's going to be hard not to do! Also, great, now I've got another research thread I have to explore - induction ranges. :) –  stephennmcdonald Aug 10 '10 at 5:22
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@roux : induction cooking works through electromagnetism; so iron, being magnetic, is great for it. Glass cookware is where you're going to run into problems. –  Joe Aug 10 '10 at 13:41
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My neighbor has a glass topped stove (formerly mine, but given up as a replacement for when we almost accidentally burned down her house with a grease fire), and a few cast iron pans that she uses all the time with no problem.

I shake the pan on the glass, and haven't noticed any scratches in the about 2 years she's had it.

If you're paranoid, see the link to Lodge's website that hobodave gave in a comment -- in it, they mention that some people have reported that they've polished the bottom of their cast iron, so make them smoother, hoping it'll make them less likely to scratch.

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I think I shall coin a new cooking phrase in your honor. "If you can't take the heat, get the fire extinguisher." –  Tim Gilbert Aug 10 '10 at 15:56
    
@Tim : see my comment under Tree77's answer on putting out grease fires at cooking.stackexchange.com/questions/3747/… –  Joe Aug 10 '10 at 16:06
    
I never even considered polishing the bottom, thanks! –  stephennmcdonald Aug 11 '10 at 1:41
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Cast iron Brinnel Hardness ranges from 110 for ductile types, up through 230 MAXIMUM for your gray iron pots, up to 440 for some more exotic cast iron alloys. Tempered Glass, such as your stove top, starts at a hardness rating of 1550 hb and goes up from there. TRY to use your cast iron skillet to scratch a piece of common or tempered glass. Use some tool steel such as a hardened steel razor scraper blade to try to scratch or cut it (hardness around 400~600. Use some abrasive steel wool or that razor to scrape your stove clean. You WON'T SCRATCH IT! YOU CAN'T!

DO NOT drop your cast iron on the glass repeatedly. If you do, eventually the same thing will happen as would happen with any other stove: You will damage it, and you will go to the hospital to be treated for you scalded body when the stuff hits the fan so to speak.

Cookware manufacturers, stove manufacturers, and cooking magazine editors are all eating out of the same money bucket. If they can do some risk management at the same time as promoting an idea that your 50 year old cast iron needs updating, they will. No lobbiest necessary, CEO #1 calls CEO #2 and the idea gets published and perpetuated.

I know, science is meaningless. It can be used to prove ANYTHING! :P

Have a nice dinner everyone, and have fun cooking it 1

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It is not a matter of melting the glass cook top, it is a matter of scratching or digging up the surface or even cracking it. You can't bang the heavy pot onto the glass - that is common sense. But with possible deep scratches it can make the stove top unsightly and difficult to clean.

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Welcome to Seasoned advice! We thank you for sharing your experience, but it was very unreadable the way you had presented it. Besides, writing in ALL CAPS is considered rude in many online communities. I re-wrote your answer using standard type and dividing it into sentences, and removed some personal opinions which were not relevant for the OP. If you are not sure what are the differences between a Q&A page and a discussion forum, please see our faq. –  rumtscho Mar 19 '13 at 17:19
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My wife just melted a teapot to the glass top. When she pulled it of, it looked like about a quarter sized piece of the enamel and some of the metal was left on the stove. I turned the exhaust fan on and the burn on high and tried to scrape it with wood as another article said to do for Aluminum. That not working, i went for a metal spatula but finally had to go for a chisel. As i teased/chipped small flakes off at a time, it finally all came of, but it looks like it pitted the glass top.

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Is this relevant? Was it actually a cast-iron teapot? –  Jefromi Feb 4 '12 at 7:36
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I am a science teacher.And durig my subject matter discussed in between students i got that glasses are harder than iron.As far as i am concerned,yes glasses are harder than iron.It's another matter that glasses are brittle so they break when hammered and iron don't as because they are non brittle.But may be in real glasses are harder than iron.As glasses can produce dark scratches on iron but iron cannot do it exactly same on the glass.

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The hardness of glass actually differs between types of glass. As a photographer, smartphone owner, glass-bowl-whipping cook and spectacle-wearer T can confirm that glass being scratched by metal objects is a frequent occurence. Even though these objects are seldom made from cast iron, I think that scratched ceran stovetops are a very real concern, no matter what a single experiment with an unknown type of glass produces. –  rumtscho Jun 5 '13 at 10:50
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