Hacker News new | past | comments | ask | show | jobs | submit login
The Pyrex Glass Controversy That Won't Die (gizmodo.com)
184 points by curtis 6 months ago | hide | past | web | favorite | 131 comments

It happens to a lot of brands. Private equity investors sniff out a name brand that has a lot of customer trust, but management that's probably weak after years of profit and not paying attention. They buy out the company and strip out all the costly materials, fire staff, sell off inventory.

The brand changes, but customers don't know it until your Breyer's ice cream has a label that says it's "frozen dairy dessert product", or your Twinkies are 10% smaller, or your Pyrex glass pans start shattering. Then you wonder what happened to your beloved childhood / family brand you trusted.

Capitalism is what happened. But things come and go, and hopefully newer, better things will take their place.

(By the way, the story of what happened to Twinkies is more interesting, and not just the negative story of a company cheapening out its product for profit's sake. There was a lot of dysfunction/waste in that product line.)

It's actually a way to avoid the efficiency of the free market. Eventually in such a market you get to a point where prices are pretty much costs due to pressure from competitors. If you suddenly and secretly reduce the cost of manufacture you can make a large amount of money up to the point that the customers catch on. You can then use this money to do socially useful stuff like create new and better products (if you wan to keep the company brand), or simply keep the money and let the company run down. Really advanced companies use the money to entrench a monopoly using the standard anti-competitive techniques (another popular way of avoiding market efficiency).

This process is sometimes known as "harvesting the brand". It is a way of usefully exploiting your customer good will..

Bought Corelle dining set which had ‘Made in USA’ printed on the box. Opened the box and the white color of the mugs doesn’t match white color of the rest of the set because they were Made in China. One of the miniscule and still very irritating thing. World Kitchen is the owner of both Pyrex and Corelle.

In my sets, the mugs are just regular ceramic mugs, whereas the bowls and plates are vitrelle (thermally bonded layers of glass).

(This was clearly written on the product description, so I knew I was getting mugs I didn't want/need as part of the set.)

We're down to the last few mugs. They seem to break more easily than our other mugs.

Just went and checked the box out, there is absolutely nothing about ceramic mugs, and lots of yada yada about Vitrelle. Not a hint that mugs are ceramic either, though you are right they are in fact ceramic. The box also has United Steel Workers (USW) logo. Deceiving is all I can say.

This is a common complaint about the mugs that come in the sets. They should make it clear that the mugs are a completely different sort of product, made in China.

That said, in my humble opinion Corelle is the best dishware ever made. There's nothing else that even comes close. They are thin, light, and super tough. We've broken only one piece in decade at my house, and that was because I absent-mindedly cut fruit on a plate using a ceramic knife, which scored the plate and lead it to snap neatly in half.

Before the Corelle we used heavy, expensive, high-class Lenox stoneware, and I fucking hated it. Plus it turned out to be contaminated with lead, which is what caused me to toss it away and switch to Corelle. My life would be significantly worse if Corelle didn't exist.

I bought two sets of these from Walmart.com: https://www.walmart.com/ip/Corelle-Livingware-Winter-Frost-W...

I remember that the Walmart product description said the mugs were different, but this was a few years ago.

Looking at the Walmart.com description today, it mentions:

"11oz stoneware mugs"

"Mugs are made from a durable stoneware material"

"Mugs are not under warranty"

Of course, I have no recollection of whether this was indicated on the box.

Well the box probably was made in the USA.

Less pedantically, I believe the rules say over half the work should have been done in the US, or something like that, so they're probably legally correct.

How much did you win in your lawsuit? I hope it was lots screw then for that.

This is basically what happened to Tim Hortons in Canada. They used to actually bake things on site, now it's all reheated from frozen deliveries of sub-par donuts and baked products.

It's been riding on patriotism and brand loyalty for 15+ years now.

At this point, though, I don't know many people who go there out of patriotism or brand loyalty.

They mostly go there because it's convenient and it's cheap enough, and quality is usually acceptable given the price. I sometimes get coffee there not because I'm expecting something great, but because I need a quick infusion of caffeine-containing liquid and Tim's is 10 meters from my front door while everything else is further.

In my mind, Tim Hortons is all about location. They're everywhere. And even if the quality is mediocre, at least it's consistently mediocre so I know what I'm getting. :)

We had a Tims counter at our high school and I fondly remember their muffins and coffee. If I'm on the road and try it again I'm quickly reminded how crap it's gotten.

The donuts aren’t even edible anymore

Heh, interesting. I saw a few of them close down near where I lived and I was curious why (though I'm in the USA, so I assumed it was more of a cultural thing vs a quality thing).

RIP Walnut Crunch

Thanks for the tip on Twinkies. I've been trying to find a good article that summarizes things. Does this one leave much you're thinking of out?


There's also this article which details some of the changes including a 94% drop in employees, primarily through automation.


Nostalgia ain't what it used to be!

Another aspect of this is the value of having trusted brand and products. It saves time to buy premium trusted brand, no research, low risk, no regrets. Until there is. Now there's a significant burden of research, and some addition risk.

This is why I stopped wearing jeans. You can either buy $150 Japanese jeans or end up with cheap, shitty jeans that blow out in the crotch within a couple months. I ended up switching to "tactical pants"--specialty cargo pants that are designed for first responders and law enforcement--and aside from having an awkwardly-sized pocket designed for carrying a spare pistol magazine, they're amazing.

I got a discounted pair of selvedge jeans from American Eagle for $30 (I think retail was $75). Amazon is also said to have good selvedge denim products. I don't understand how you're ripping your crotch after only a few months of usage: that's never happened to me.

Well, (a) I bought Levis (maybe that was the real mistake), and (b) I'm a fatass.

My Wranglers bought at K-Mart have held up well.

K-Mart still exists???

I think if manufacturing process changes significantly (lord help laywers define "significantly") it should be considered a fraud to not notify customers in clear and explicit manner.

the tolerance of the glass is on the box, right? so every customer should be able to compare it with other products before purchasing.

if it just says "shatterproof" or "break resistant", then that is rather vague of course, but that should be a warning in itself. (of course, brands are a thing, we are lazy after all, an re-evaluating products every time seems like a waste of time)

By tolerance, you mean heat rating? The truly telling parameter would be CoE, coefficient of thermal expansion, which would be 33 for borosilicate and about 90 for soda lime glass. That’s probably considered too technical be specified on a consumer kitchen box, though.

Not exactly. You say that tolerance was, let's say 20, and it was written on the box, but now it is 10, and it is written on the box too.

I say that it should be "10 (but was 20 a year ago)" and no fine print allowed for second part.

Would you like to borrow my grandfather's axe?

I use a spade my father purchased when he was a young man. It's end is rounded from use but it is still the strongest digging tool I have. He was born in 1930. The metal is corroded and the wooden handle is heavy but I just feels so good to work with. I've considered replacing it but everytime I pick a new one up in a store it just feels like a child's toy.

A few flavors of Breyer’s (vanilla, chocolate, mint chip) I believe are still labeled “ice cream” and have ingredient labels to back it up.

Protip: You can tell soda-lime from borosilicate by using a homemade polarimeter. [1] Get a pair of polarizing sunglasses, and hold them in front of a computer monitor at such an angle that the screen looks black. Hold the cookware in between the glasses and the screen. You should now be able to see the screen (see my synchronicitous comment [2] yesterday about the link here to quantum mechanics). If you see a checkerboard pattern, you are holding tempered soda-lime. (The pattern is due to the tempering process.)

Soda-lime also has a distinctive greenish tinge when viewed edgewise. Borosilicate is clear.

[1] https://arstechnica.com/civis/viewtopic.php?p=2746878#p27468...

[2] https://news.ycombinator.com/item?id=19406122

That's wild, thanks! I tried with a couple of my pieces (although they do say "not polarimeter safe") and they did have some noticeable brightness gradients, though I hesitate to call them patterns.

What DID stand out looked like brown scorch marks or stellar jets/magnetic poles. I don't think they were really scorch marks, but it was striking just how brown that tiny area was.

Edit: got a picture but it's more of a red and blue interplay than just brown.


Maybe it's the rgb of the monitor. And I have seen similar colors in windshield polarization. It makes more sense if you rotate the glasses and watch the brown and blue flow through the patterns

That's definitely soda-lime. (Judging both by the pattern and the logo.) The reason for that pattern according to the source I linked above is that that is the shape of the air jets used for cooling the glass during tempering. Windshield glass shows the same patterns for the same reasons.

"Not polarimeter safe" is probably a reliable indication of an inferior product.

Polarimeters aren't dangerous; they must want something to complain about when someone uses one to prove their product is inferior.

Cool tip about the polarization.

As far as visual ID, I don’t know about the borosilicate that was used for a kitchenware, but borosilicate can appear green, colorless or slightly yellowish. It depends on the formulation and impurities in the batch – for instance, iron causes the green color. This varies between Kimax and Pyrex and Duran used for labware and art.

One could also distinguish this glass by using the index of refractivity. Glass will disappear when put into liquid with the right refraction. You can make a formula with a refractive index that matches a known glass and then compare. I’d post links but I’m on a very slow connection.

What does the polarimeter test imply if neither of the described results happens? The glassware in my house doesn't seem to have any noticeable effect on the polarized light; it doesn't get more visible or have any particular pattern.

I am far from an expert, so take everything I say with a grain of salt. But my understanding is that what makes light visible in the polarimeter test is stress due to tempering. E.g. my soda-lime (Pyrex) bakeware shows up very clearly in this test, but my soda-lime drinking glasses do not cause any light to appear in the test (except at their bottom).

I unfortunately don't own borosilicate bakeware, so my above description of the effect comes from my linked source. The only borosilicate samples I do have are a microwave dish and a candy thermometer. The microwave dish (which has a rough texture) does show some light, but in a hazy pattern, and much less than soda-lime bakeware. The candy thermometer (which is test-tube sized) shows no light in the test.

So if you're looking at bakeware, it's probable that it's either borosilicate or some other type (such as aluminosilicate used in Pyrex Flameware… again just guessing here). If you're looking at drinking glasses, then they're probably just untempered soda glass or crystalware (lead glass).

Thanks! For what it's worth I was looking at glass bakeware that advertises itself as heat resistant and microwaveable, from a company called Iwaki glass. Googling suggests they make a lot of borosilicate scientific stuff but I couldn't find any info about their consumer products.

Step-by-step instructions:

1. Buy some sunglasses. Make sure they have polarizing lenses.

2. Get a computer monitor.

3. Holding the glasses in front of the screen, rotate them until the angle is such that the screen appears black when looking through the lenses.

4. Make a note of the angle. In this configuration, the combination of the glasses and the screen serves as a homemade polarimeter.

5. Throw all that shit in the garbage.

6. Just look at the glassware edgewise, if it's greenish it's soda-lime.

But using a homemade polarimeter is way cooler.

You're missing the point.

It's fun and is a great way to see an example of polarization in the real world.

> Corning employee Jessie Littleton discovered a new use for the material after his wife Bessie used a sawed-off borosilicate glass battery jar for baking.

Sounds more like Bessie discovered the new use, not Jessie.

EDIT: The Corning Museum of Glass credits them both- while noting that it was Jesse’s idea to try it.


Incidentally the Corning Museum of Glass has an a YouTube channel worth checking out. They have a bunch of long, well-shot glass artists doing some incredible work, start to finish- good videos to play in the background while working on other things.

I second that, the CMOG channel is great. They have high production quality (especially consider the constraints of the glass shop) and really talented artists / craftspeople.

Bill Gudenrath's series on Venetian glassware is particularly fun because he's such a craftsman but also a fascinating teacher.

If you want proper Pyrex, just go to ebay or a European site, and find British (second hand) or French Pyrex.

It's all still borosilicate glass. Helpfully the brand logos are slightly different for the different countries, so it should be easy to spot.

It seems daft to me to take away the main selling point of the stuff by starting to make it with cheap glass.

EDIT: Infographic with dates and the different logos: http://www.biggreenpurse.com/wp-content/uploads/2016/01/Pyre...

If you want proper borosilicate glass, just go to a company that has been honest with their branding.

I've found SIMAX (https://www.kavalier.cz/en/simax-home.html) to be a good one personally. Made in the Czech Republic by a glass company that still makes labware, and as best I can tell, everything they make out of glass is borosilicate. Even the flower vases.

How can you tell? It says made in czech rep but nothing about type of glass.


"Simax glass ranks among the types of glass of the group of clear „hard“ borosilicate glass „3.3“, which excel in a high heat and chemical resistance and which are defined by international ČSN ISO 3585 Standard. It complies to the full with the properties prescribed by these standards."

Or go to any store when you happen to be in Europe. My local department store has an extensive range of bakeware and there are ~50% cheaper brands using borosilicate glass that have performed well for me. They're easily identifiable as they label themselves for thermal shock resistance.

"Based on reports made to the company and the Consumer Product Safety Commission, less than one tenth of one percent of the millions of Pyrex products sold each year experience thermal breakage"

So, that's potentially thousands of people experiencing this each year? Not a record I would be proud of....

Also, how many people bother to report a broken baking dish or whatever? Figure the reality is at least 10x worse.

I had a Pyrex pan shatter. Didn’t bother reporting of course.

I also had a Pyrex bowl shatter and didn’t report.

I bought a new one and am careful about how I heat it now.

I had a Pyrex baking pan crack in the oven once. I was baking some chicken breasts that I hadn't thawed, they were still frozen solid. The pan didn't explode though, just cracked into a couple of large pieces.

I recently bought a set of pyrex containers. The temperature safety procedures are irritatingly complex. Frozen chicken in a hot oven doesn't surprise me that much, but you can't even use it to put room temperature ingredients in the oven while it's preheating.

This is my small batch, artisanal data: As an avid baker and engineer, over the last decade I've had two pieces of cast iron catastrophically fail vs one piece of borosilicate. I'm not sure if that makes metal twice as dangerous, or if people maybe report things breaking disproportionately to the manufactured volume...

I will say feeding my future father in law a glass casarole was not a strong move.

> I've had two pieces of cast iron catastrophically fail

How does cast iron fail? Was this like a cast iron pan or an enameled dutch oven?

Cheap cast has impurities causing expansion rate differences. Cast being brittle will cause that to pop. Also one of the reasons brazing cast is not straightforward

I’d just like to point out that I have and broke Pyrex, not borosilicate (as explained by the article).

Oh interesting. We've lost several pyrex dishes. The first was nine or ten years ago. My wife was baking a raspberry crisp thing (or some red fruit), and the dish cracked into hundreds of little bits before we took it out of the oven. Each bit had sides maybe half a centimeter long. It certainly wasn't caused by a drastic temperature change, unless you count opening the oven. It is very unnerving for your dessert to turn into shards of broken glass. I hope this article gets a wide audience, and business goes to a more deserving company.

The glass probably had a scratch at a stress point. It doesn't take much for a slight thermal shock for it to explosively decompose at that point.

Oh, so maybe these people are using knives to cut things out of the pans, which causes the initial cracks in the glass.

Thanks for the article. I was looking to replace a chipped old Pyrex measuring cup about a month ago and found myself going down this same rathole of research.

It all makes perfect sense as I just naturally assume that all old-school US consumer goods go through the same sequence of events:

1) sell the company, close US factory 2) license the name to a manufacturer in China 3) cost reduce, cost reduce, cost reduce 4) profit!

You could make a good BOLTR-like youtube channel by weighing and measuring changes over time in common products. The KitchenAid mixer would be a good one.

AvE has one video on the KitchenAid, if I recall correctly he was actually surprised that it was still pretty well-built.


In the early 2000s there was a lot of talk about KitchenAid switching to plastic gear housings. They switched back after a few years either due to backlash or warranty issues.

Here's a cool comparison of wahl hair clippers from 50 years ago and a modern pair:


> due to backlash or warranty issues.

I see what you did there. I suspect it was unintentional, but it’s quite pleasing nonetheless.

I had one. It broke just outside of its warranty period. I opened it up. Plastic gears and complete junk inside of a tough-looking metal housing. Same with their blender; broke pretty fast, with relatively mild use.

It depends on which model you get. I think lower-priced models are mostly plastic gears, but the video I linked is the professional model. Those use metal gearing etc.

That's my guess. The model most people have is not the one that AvE took apart.

To do a proper review, you'd tear apart an early mixer that was from the Hobart era in addition to one from 25 years ago.

Most of them are still made in a factory in Greenville, Ohio.

> ... and found myself going down this same rathole of research.

Surely you meant rabbit hole, not rathole.

In the case of the time wasting abilities of the internet, it's a rathole.

Wishful thinking in the article. They say:

Amazon Basics sells a pair of borosilicate glass pans for $15.

But clicking on the link to those glass pans finds review comments like this:

"These are not borosilicate"

"glass will crack after minimal use"

"Broke first use"

I've never bought an AmazonBasics product, and I don't think I'm going to start any time soon. In my mind Amazon now stands for "cheap" and "counterfeit". Not a brand name I want to trust any more.

The internet is about 50/50 lying companies and idiot users. Amazon likes to consolidate reviews for different products, versions, and sellers together, which makes it impossible to know what you're gonna get without actually ordering it.

It's true that borosilicate Pyrex is better than the newer stuff, but honestly both are inferior to stoneware, cast iron or stainless steel. You will not find any professional kitchen cooking in glassware.

Borosilicate glass (and some aluminosilicate glass-ceramic) is transparent, doesn't leech iron or nickel into the food, is easier to clean since limescale doesn't bind easily to it, doesn't rust when exposed to salty water, can be used in a microwave oven, unlike cast iron and stainless steel.

The only disadvantage is that it shatters if you drop it or hit it with enough force.

Stainless steel shouldn't leech anything into your food, no matter what's inside it. (It's used to store many kind of acids, and doesn't leech anything into those. I hope your food is tamer than pure fluoridric acid, for example.)

But there is a lot of stuff labeled "stainless steel" that stains. Sometimes even before you buy it.

Iron is a nutrient, though.

Indeed, and cast iron pans are specifically employed by vegans for the dietary iron they provide.

You probably won't find professional kitchens using stoneware, the only exceptions I can think of would be things like tagines, where its more down to cultural baggage, than inherent properties of the material. I'm not sure you'd find much cast iron either, who wants to be lugging around cast iron all day.

Use in professional kitchen doesn't prove some underlying superiority, its just a different set of optimisations.

I want to make a caserole, fry on hob, then in the oven, in a dish that I can present on the table, put the leftovers in the fridge, and be able to put the container back in the oven or microwave to reheat. That isn't what a professional kitchen is optimising for.

The overall best glass is probably fused silica. I doubt you can find it for anything other than high-end lab gear.

The best glass for shatter resistance is the stuff used for large telescope mirrors, but that too would be expensive and I think somewhat easy to scratch. The scratch resistance would dramatically improve with a sapphire coating, as is done on the laser scanner windows in supermarket checkout lanes.

Metal doesn't really qualify if you want something transparent. I've noticed that it is very difficult to find stainless steel that is polished on the inside. The outside is normally polished, but I'm seldom trying to clean food off of the outside.

> Metal doesn't really qualify if you want something transparent.

Well, there's Aluminium oxynitride aka ALON aka "Transparent Aluminium". Probably a bit expensive for cookware, though.

The "transparent aluminum" thing really needs to die. By the same logic you could just call normal glass "transparent silicon"...

You could call lead crystal (aka crystal, which people often think is something other than glass) transparent lead by the same token. It’s 40 to 60% lead oxide by weight.

Fused silica, aka quartz, is also employed widely in the cannabis industry. Cannabis concentrates are typically vaporized, or dab, from quartz ‘bangers’ or ‘nails’. Google Quave Club Banger or Joel Halen for more info.

But glassware can be used in microwaves, and metal can not. I don't cook in glassware, but I very frequently heat food in glassware.

Metal actually can be used in a microwave safely. For example, sheet pans with rounded edges and metal bowls are quite safe, as long as you have a decent amount of something in those containers to absorb any energy that the metal reflects. Plenty of prepackaged meals found in grocery stores have a thin sheet of metal in the packaging to change the way the meal heats up in the microwave.

Things like crumpled aluminum foil, a metal fork, or random bits of decorative metal in a dish could cause electrical arcing because charge can build up on the "edges" (e.g. the tines of a fork).

Of course, it's more convenient to use something like glass because we just don't have to give it a second thought (aside from the whole exploding glass problem). And for that, it's reasonable to simply avoid putting any metal in a microwave.

Microwaves might convenient but are inferior to conventional ovens. You won't find one in a professional (high end) kitchen.

Do you happen to have a source for this?

One can find articles that seem to imply the opposite.

> A few of Mr. Myhrvold’s microwave recipes — an eggplant Parmesan, which purports to turn the vegetable creamy instead of rubbery, and a steamed chocolate sponge cake — echoed ones I had seen before. (Mark Bittman has written in The New York Times about using the microwave to make several dishes, and “Eleven Madison Park: The Cookbook” includes a recipe for microwaved pistachio spongecake.)


Despite that he wrote an elaborate technical cookbook, does anyone from the gourmet chef world really consider Nathan Myhrvold an authority on cuisine or cooking techniques or taste?

Many chefs in high end restaurants won't accept a microwave. Michel Roux Jr even complained when contestants used them on British TV show Masterchef.

If you want to start name dropping, what about Heston Blumenthal? I bet he has a microwave.

I'm sure some chefs reject microwaves to make a point. I would contend its a minority though, I would also contend that it's to allow the Mr Rouxs of the world to justify inflated prices, rather than any inherent problem with the machine.

Chef Ping is found in plenty of high end kitchens; I know plenty of chefs who use them from pubs right the way up to two star kitchens.

Hell, even some of the sponge cake on the menu at el Bulli was microwaved.

When microwaves were fairly novel, contemporary cookbooks and magazines acted as if future Americans would be cooking all foods in the microwave. From what I recall, my mother cooking pork roast in the microwave did not last very long.

Depends...if it is just you and your partner, cooking a couple of meals per week but also eating out a lot and not cooking for children/other housemates? Go for the glassware if you like the looks. If you're cooking frequently or intensely, go for the steel options for durability plus ultimately versatility

Yet another casualty of moving production to China. I knew one of the Corning execs who headed up moving everything to China and setting up the factories over there.

At the time, regulatory costs in US were crazy, so plenty of motivation. For example, if an accident occurred in a single factory, OSHA would make all Corning employees everywhere go through training about it, even though the accident involved equipment and processes that only existed at the one plant.

This is very timely because I had a Pyrex-type glass lid explode on me today. It was a lid to a Calphalon frying pan,and I was grilling a veggie burger and some onions. I put the lid on and set told Alexa to remind me in 2 minutes.

Just before the alarm sounded: "BOOM" and there were a thousand little pieces of glass everywhere.

I've had this happen when I've heated it unevenly, or when I accidentally put cold water on a hot container, but never in normal use.

I'm wondering if Pyrex hasn't changed, but if cook tops have. Are they hotter or less even than cook tops of the past?

Pyrex has definitely changed, in the US at least. Pyrex-branded cookware is no longer made out of Pyrex (borosilicate glass). Which is particularly shameless because the whole reason for Pyrex is that ordinary soda-lime glass, which they're making it from now, isn't suitable for this purpose because its high coefficient of thermal expansion makes it shatter.

Pyrex has changed; it's not a conjecture. Modern Pyrex is physically and verifiably a different material than traditional Pyrex.

The lawsuit against those researchers was particularly shameless, in my opinion. Will avoid products from this company in the future.

My brother once cut his hand badly when an IKEA glass shattered in his hand while washing it. (Either he was washing a cold glass in hot water, or a hot glass in cold - I forget which).

It resulted in a trip to the hospital for stitches and his still has the scar.

I think they've improved these days, but there was a period where certain IKEA glasswear was very prone to thermal shock.

I've had this happen to a friend except it was stacked on top of each other. Trying to pull it apart when stuck ended up breaking the glass with the shard going into their hand.

The link to safety instructions goes to a geofenced 404 for me in UK. Who puts safety instructions behind a geofence? Somebody scared of European consumer laws, that’s who. Not a good look...

The European product is different to the American product, so it does make some sense.

As an American spending the last several months in the EU this is infuriating. So much so I setup a VPN simply to read the news. It seems the default method of dealing with GDPR is to simply geofence.

John C. Mauro does some really cool work, if you're interested in the underlying statistic mechanics of glass, and how to use computers to design better glass.

I was doing the melt pepto bismol into bismuth experiment and using a rosebud oxy acetylene tip and found some of the soda lime kind. Also demonstrated why safety glasses are important.

That much temperature caused a pretty good boom with shrapnel when the glass exploded

More interesting to me is the same issue with CorningWare[1]. I've used this for microwaving food for decades and I've bought a lot of it off ebay. In fact, that's all I've used ebay for in the last 10+ years. According to the wikipedia page, it suffers from the same borosilicate vs soda-lime issue.

[1] https://en.wikipedia.org/wiki/CorningWare

Corning is one of the companies they are discussing in the article

To be clear: it's the lids that would involve this issue, not the Corningware pieces themselves. Those are a glass ceramic (a kind of glass converted, by heating, to a microcrystalline ceramic.)

Is it possible to buy new aluminosilicate glass dishware commercially?

For some reason I really want to try cooking directly over a flame with a glass pot.

No you don't. Glass is nearly the worst possible material for stovetop cooking. With thermal conductivity roughly 1/70 that of cast iron, it's impossible to cook on a range without burning the food, and that combined with a relatively low heat capacity makes it useless even for searing. On top of that, glass seems to be a uniquely sticky cooking surface. It's far stickier than unseasoned steel or aluminum.

I have several pieces of Visions. I would never, ever use them on a range. I use them exclusively in the oven, where the IR transmittance of the glass is useful, and the uniform surrounding temperature makes the poor thermal conductivity a non-issue.

How does lower thermal connectivity cause the food to burn easier?

FWIW, when I was a kid we had pyrex bowls with clip-on handles for stovetop heating. Yes, you wouldn't cook with it, but great for re-heating food.

Presumably it causes food to burn easier because the areas directly touching the flame/heating element become the temperature of the heating element, rather than spreading the heat out across the surface of the container.

Yeah that makes some sense, but I'm skeptical. Like the sibling comment here, I have glassblowing experience and intuitively since glass changes temperature more slowly it is naturally less prone to hot spots. Also, it is generally thicker than most metal cookware which means more distance between the heating element and the food to disperse the head. Speaking from experience, touching a 250°C oven heating element will generally burn you worse than touching 600°C borosilicate glass, strong spinal reflex from the former notwithstanding.

> ...intuitively since glass changes temperature more slowly it is naturally less prone to hot spots.

You've got it backwards. This is a well-known principle in cookware construction, and it's the whole reason that copper and aluminum clad cookware exists. Al and Cu spread heat more quickly, and thus farther across the pan body before it's conducted or radiated away. Remember that the heat isn't just building up in the pan forever; it's dissipated nearly as fast as it's supplied. The heat is conducted to the food in the pan, and in the case of glass it's also being quickly radiated away due to the material's high emissivity and transparence to IR at low-single-micron wavelengths. Thicker glass is generally even worse just because it takes so long to heat up, so the parts that are farther from the flame never reach cooking temperature, while the closer parts are scorching hot.

Look up any review of cookware where they use thermal imaging, and you'll the see the results of thermal conductivity on heating evenness. A pan that uses a lot of aluminum or copper will have a much more evenly heated surface than a pan made only of cast iron or steel. And glass is a hundred times worse yet.

I don’t have much experience with cooking, but this sounds correct to me from what I know about thermodynamics. After all, air has much less thermal conductivity than glass, but if you stick a potato over an open flame you expect a spot on the potato to burn, rather than all the air to slowly heat up and heat the potato evenly.

In fluids like air, heat transfer is dominated by fluid flow, in the form of convection in the case of cooking over an open fire.

It's useful to think of a piece of cookware as a kind of radiator, because that's essentially what it is. Heat is transferred to food by direct contact, but also by radiation. Pots and pans are shaped perfectly to maximize both radiation and conduction by contact, and thus they experience a very high rate of cooling. This means that if you want evenness of heating, then high thermal conductivity is necessary in order to keep up with the heat loss.

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.

> 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.

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).

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. High speed video of one of these things exploding. Kinda blew my mind.

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?

Here (Italy) it is common enough to use "Pirex" (actually "Luminarc", however "real borosilicate") glassware normally on gas (methane) stoves, you need to use a small net like this one (example):


or (a more recent/new design) like this one:


try VISIONS or Luminarc

Gently stirring with your new hammer shaped ladle?

Reminds me of an experiment in my undergraduate glass lab. Take soda-lime stirring rods and break 50 or so under 4 point bend test. Record strength.

Take another batch and simply log-roll them along the lab bench for half a meter. Repeat break test. Note the reduction in strength signficant at p=0.05 .

Fracture toughness is a bear.

The “pleasing heft” the article mentions is a sign that you have soda-lime glass instead of borosilicate. A few years ago after having a 2-cup soda-lime Pyrex measuring cup explode I order the equivalent from Arcuisine in borosilicate and I was amazed at how much lighter it was.

That sucks, I bought Pyrex specifically because I thought it was borosilicate. Never another Pyrex for me. I assume my Pyrex labware is ok.

Frankly you could go through life assuming any company that sues for "defamation" is the bad guy and me right 95% of the time.

>parent company of Pyrex among others, is planning to merge with Instant Brands, maker of the very popular Instant Pot.

Talk about a highly advertised product.

Before Instant Brands starts spamming 'Mom posts', about how great Pyrex is, expect it to be heavy and burn your hands if it gets hot. My tupperware isnt like this.

Advantage I see for glass is that it’s rather inert, so you never have to worry about BPA or whatever else leaching into your foods, or it catching on fire or melting. Harder to abrade Pericles into your food.

Also, glass can be scrubbed entirely clean, unlike plastic. When I was diagnosed with celiac disease, I had to throw away most of my dishes that were not glass or metal.

Disadvantages of glass clearly include fragility.

Applications are open for YC Winter 2020

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact