So, the other day, while I was struggling to clean a particularly stubborn stain from the inside of a 2 quart teapot (P-105), the proverbial "light bulb" went off over my head.
This teapot is pristine on the outside, not a mark, not a scratch.... nothing.
Inside, however, is a different story. Oh, it's clean.... Especially after I finished with the Barkeepers Friend and then heated up Oxyclean in it and let it soak for 24 hours... But there were still grey "spots" in the bottom. Thinking they might be hard water stains, I then soaked with CLR for 24 hours. They were still there. So, in desperation I decided to try the Pfaltzgraff Cleaner, even though I was pretty sure that they weren't utensil marks... How would you get utensil marks in the bottom of a teapot? Especially round blotch utensil marks. Well, the Pfaltzgraff cleaner didn't do anything either, the spots are still there......
So, I took a closer look at the 2 annoying spots in the bottom.
Closer...
A little closer.....
THERE, that's close enough. Can you see it too? Is it translating well in the photos? The "grey" looks like it's slightly translucent. You can still see "white" swirled around within this translucent spot. My working theory is that these are spots that have vitrified.
OK, maybe I should take a step back for a second and do a little explaining.
When you melt something like, say Sugar, on the stove and it becomes an amber liquid, then you pour said liquid onto a sheet pan and allow it to cool, you have not only formed a hard caramel, you have "vitrified" sugar. Basically, creating sugar glass. This happens with rocks as well. Obsidian, for all intensive purposes, is a vitrified "rock". ALL rocks, when exposed to intense heat, will vitrify to some degree.
All it really means is that something is melted and cooled in such a way that it remains in an amorphous state instead of re-crystallizing. Some amorphous mixtures allow more light to pass through them than others. Such is the case with a mixture of Sodium Carbonate (Soda), Calcium Oxide (Lime), and Silicon Dioxide (Silica Sand); better known as Soda-Lime Glass.
Corningware is based on the DE-vitrification of glass. Meaning, that it is purposefully crystallized to make "Ceramic-Glass". This, however, happens after the glass has first been formed and is in an amorphous state.
The difference is that the glass used to make Corningware has been "seeded", in this case with Titanium Dioxide, so that when the glass piece is heated treated, after the initial forming, the Titanium Dioxide forms millions of little nuclei. This nucleated glass is heated again and crystals form around the nuclei. The amount of crystal growth depends on the temperature it is heated to and the duration of the heating. There you have it, the purposeful de-vitrification of glass. Pyrex Opal Glass uses some of this same principals but the crystal content is significantly less than that of Corningware, being less than 10%. Pyrex Tempered Opal Glass (as in mixing bowls and such) are also not formed of Borosilicate, it's a tempered Soda Lime Glass (always has been) and, I believe, it is seeded with Tin Oxide.
In the case of this teapot, I think that it was boiled dry one too many times on the stove, and these areas have UN-crystallize, turning back into glass. Basically, its vitrified. At least in those spots. Mind you, this is made of "Borosilicate" low expansion glass to begin with, so I don't think it really harms anything. It just looks weird on the inside.
As far as why it is ONLY on the inside and not on the outside, I think that has to do with the way that heat moves through and radiates from an object... There were, more than likely, minerals in the water that was being boiled dry that may have had something to do with it as well.
But my theory doesn't extend any further at this point, and I honestly think I pulled a muscle in my brain as it is. ;-)
Where is your Corningware??
~~
Closer...
OK, maybe I should take a step back for a second and do a little explaining.
When you melt something like, say Sugar, on the stove and it becomes an amber liquid, then you pour said liquid onto a sheet pan and allow it to cool, you have not only formed a hard caramel, you have "vitrified" sugar. Basically, creating sugar glass. This happens with rocks as well. Obsidian, for all intensive purposes, is a vitrified "rock". ALL rocks, when exposed to intense heat, will vitrify to some degree.
All it really means is that something is melted and cooled in such a way that it remains in an amorphous state instead of re-crystallizing. Some amorphous mixtures allow more light to pass through them than others. Such is the case with a mixture of Sodium Carbonate (Soda), Calcium Oxide (Lime), and Silicon Dioxide (Silica Sand); better known as Soda-Lime Glass.
Corningware is based on the DE-vitrification of glass. Meaning, that it is purposefully crystallized to make "Ceramic-Glass". This, however, happens after the glass has first been formed and is in an amorphous state.
The difference is that the glass used to make Corningware has been "seeded", in this case with Titanium Dioxide, so that when the glass piece is heated treated, after the initial forming, the Titanium Dioxide forms millions of little nuclei. This nucleated glass is heated again and crystals form around the nuclei. The amount of crystal growth depends on the temperature it is heated to and the duration of the heating. There you have it, the purposeful de-vitrification of glass. Pyrex Opal Glass uses some of this same principals but the crystal content is significantly less than that of Corningware, being less than 10%. Pyrex Tempered Opal Glass (as in mixing bowls and such) are also not formed of Borosilicate, it's a tempered Soda Lime Glass (always has been) and, I believe, it is seeded with Tin Oxide.
In the case of this teapot, I think that it was boiled dry one too many times on the stove, and these areas have UN-crystallize, turning back into glass. Basically, its vitrified. At least in those spots. Mind you, this is made of "Borosilicate" low expansion glass to begin with, so I don't think it really harms anything. It just looks weird on the inside.
As far as why it is ONLY on the inside and not on the outside, I think that has to do with the way that heat moves through and radiates from an object... There were, more than likely, minerals in the water that was being boiled dry that may have had something to do with it as well.
But my theory doesn't extend any further at this point, and I honestly think I pulled a muscle in my brain as it is. ;-)
Where is your Corningware??
~~
