4 ms·

I would think the dense mass of the pan slowly becomes hot and holds a fair bit of heat. This should be a fairly gentle way to cook, but have the same disadvant

I would think the dense mass of the pan slowly becomes hot and holds a fair bit of heat. This should be a fairly gentle way to cook, but have the same disadvantages of an electric stove top versus gas - slower to respond to range setting changes. When you turn the stove down the glass would take longer to radiate the heat it absorbed into the food than metal would. Not sure about the mass of typical pans of each material, or heat retention potential of glass vs steel/copper. Slower response to lowering heat could cause food to be burnt. I haven’t used glass cookware, though I always thought it looked cool as a kid. I do have 20 years of glassblowing experience though.

nate_meurer 8y ago
> I would think the dense mass of the pan slowly becomes hot and holds a fair bit of heat. It doesn't work that way. The thermal conductivity of glass is so low, the heat doesn't have a chance to spread before being lost to radiation and conduction to the contents of the pan. Glass has high emissivity, and it's at least somewhat transparent, so heat rapidly radiates from the whole bulk of the material. The result is scorching hot spots directly over the flames or coils, while the rest of the pan remains too cool to cook. Glass also has relatively low volumetric heat capacity, meaning a layer of glass holds much less heat than the same thickness of steel or aluminum. Glass really has the worst combination of characteristics for stovetop cooking. There's a reason nobody uses it.
- code_duck 8y ago
  Makes sense that it would be hottest directly near the flame source - the low conductivity assures that. I’m sure this would be clear if I tried it. Some in the glass community cook in 110 mm tubes of Pyrex at parties. This is also a commercial product (baking cylindrical loaves!). The tubes are rotated like a rotisserie, and the glass is very thin. It works quite well, but we don’t tend to do this outside of glassblowing camp. As far as the thickness, the glass pans are much thicker than typical metal pans, probably for that reason as well as many others. I have some metal pans that are maybe 2mm and they are awful about hot spots. I think the glass pans are about twice as thick as my cast iron Dutch oven, but we’d have to measure. I think the worst aspect is chipping - one chip and the whole thing should be thrown away (one could flamepolish and anneal it, but that’s unlikely for consumers).
  - nate_meurer 8y ago
    Interesting. I love glass blowing. Maybe I'll learn about it some day. Borosilicate and aluminosilicate cookware is actually pretty tolerant of chipping, because pieces tend to be thoroughly annealed. Tempered soda-lime, on the other hand, is not, so it has tremendous internal stress that makes it much tougher than borosilicate, but once it does chip it's liable to shatter explosively. Like Prince Rupert's drops. Hey, you want to see something cool? You'll appreciate this since you work with the stuff. Go to 2 min 45 sec in the video at https://www.youtube.com/watch?v=xe-f4gokRBs https://www.youtube.com/watch?v=xe-f4gokRBs. High speed video of one of these things exploding. Kinda blew my mind.
    - code_duck 8y ago
      PR drops are definitely fun! You can make them easily with a torch, some glass and a bow of water. The problem with chips in a lid is that they will slowly expand over time, likely leaving debris in food. It can also lead to sudden unexpected failure as glass gets much weaker once chipped or scored, especially combined with moisture. I don’t discard lids immediately either, but the manufacturers do suggest it for those reasons. Definitely not like tempered glass, you’re right! Tempered glass is safer in how it break into those little square pieces - much less likely to lacerate than long jagged shards, in many applications (shower doors for instance). I had a tempered safety glass oven door shatter suddenly one day - apparently this happens fairly often?

nate_meurer 8y ago

> I would think the dense mass of the pan slowly becomes hot and holds a fair bit of heat. It doesn't work that way. The thermal conductivity of glass is so low, the heat doesn't have a chance to spread before being lost to radiation and conduction to the contents of the pan. Glass has high emissivity, and it's at least somewhat transparent, so heat rapidly radiates from the whole bulk of the material. The result is scorching hot spots directly over the flames or coils, while the rest of the pan remains too cool to cook. Glass also has relatively low volumetric heat capacity, meaning a layer of glass holds much less heat than the same thickness of steel or aluminum. Glass really has the worst combination of characteristics for stovetop cooking. There's a reason nobody uses it.

code_duck 8y ago
Makes sense that it would be hottest directly near the flame source - the low conductivity assures that. I’m sure this would be clear if I tried it. Some in the glass community cook in 110 mm tubes of Pyrex at parties. This is also a commercial product (baking cylindrical loaves!). The tubes are rotated like a rotisserie, and the glass is very thin. It works quite well, but we don’t tend to do this outside of glassblowing camp. As far as the thickness, the glass pans are much thicker than typical metal pans, probably for that reason as well as many others. I have some metal pans that are maybe 2mm and they are awful about hot spots. I think the glass pans are about twice as thick as my cast iron Dutch oven, but we’d have to measure. I think the worst aspect is chipping - one chip and the whole thing should be thrown away (one could flamepolish and anneal it, but that’s unlikely for consumers).
- nate_meurer 8y ago
  Interesting. I love glass blowing. Maybe I'll learn about it some day. Borosilicate and aluminosilicate cookware is actually pretty tolerant of chipping, because pieces tend to be thoroughly annealed. Tempered soda-lime, on the other hand, is not, so it has tremendous internal stress that makes it much tougher than borosilicate, but once it does chip it's liable to shatter explosively. Like Prince Rupert's drops. Hey, you want to see something cool? You'll appreciate this since you work with the stuff. Go to 2 min 45 sec in the video at https://www.youtube.com/watch?v=xe-f4gokRBs https://www.youtube.com/watch?v=xe-f4gokRBs. High speed video of one of these things exploding. Kinda blew my mind.
  - code_duck 8y ago
    PR drops are definitely fun! You can make them easily with a torch, some glass and a bow of water. The problem with chips in a lid is that they will slowly expand over time, likely leaving debris in food. It can also lead to sudden unexpected failure as glass gets much weaker once chipped or scored, especially combined with moisture. I don’t discard lids immediately either, but the manufacturers do suggest it for those reasons. Definitely not like tempered glass, you’re right! Tempered glass is safer in how it break into those little square pieces - much less likely to lacerate than long jagged shards, in many applications (shower doors for instance). I had a tempered safety glass oven door shatter suddenly one day - apparently this happens fairly often?