Is Pyrex all right for one use?

Hey all,

I thought I was ready to make my first little batch, and my lye is finally arriving this afternoon. I did tons of research - but somehow until now I managed to miss the fact that Pyrex is weakened by lye. I think it was because in all the cp-making videos I watched, the demonstrators used Pyrex (or even, in some cases, glass jars!). I believe I have seen Pyrex recommended in lists of required supplies as well.

I've been waiting for a long time until I felt prepared to do this, so of course I'm impatient, but I also want to be safe. I probably won't be able to go and get stainless steel bowls until the weekend. In your honest opinions, do you think I could make my first small batch using my Pyrex, and thereafter only use my Pyrex for safer stuff such as mixing body butters or infusing oils?

I'm honestly not sure how much of a risk it would be. Obviously I'm hoping you'll say it'll be fine, but if the general consensus is 'no', then I will bow to your greater knowledge and wait until I can get the stainless steel.

Thank you all for your advice!

- Laurence

My comment may get some grimaces, but I use my Pyrex bowl for my oils and batter mixing. I make my lye solution in a safe plastic jug, but I do pour my lye solution into my Pyrex bowl to mix with my oils. I've been using the same Pyrex bowl for years without issue. The batter is only in my Pyrex bowl for a max of 15-30 minutes while I stickblend and pour. It's then wiped out with paper towel and immediately washed and dried. It still looks brand new, I don't see any etching. I know I may be pushing my luck and I've heard the horror stories, but I've never had an issue.

I would not use stainless steel either, I would use plastic with a recycle 2 or 5 number on it. I use these:

http://www.homedepot.com/p/HDX-1-qt-Multi-Mix-Pail-2M3/202264024

you can get them at wal-mart or anywhere that has a paint area.

toxikon said:

My comment may get some grimaces, but I use my Pyrex bowl for my oils and batter mixing. I make my lye solution in a safe plastic jug, but I do pour my lye solution into my Pyrex bowl to mix with my oils. I've been using the same Pyrex bowl for years without issue. The batter is only in my Pyrex bowl for a max of 15-30 minutes while I stickblend and pour. It's then wiped out with paper towel and immediately washed and dried. It still looks brand new, I don't see any etching. I know I may be pushing my luck and I've heard the horror stories, but I've never had an issue.

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Fully prepared for the flaming, I do exactly the same thing. I know it's not best practice and I don't recommend it for anyone else, but I feel safe enough doing it.

ETA: In re-reading, I want to emphasize that my comment was not meant as a go-ahead for Lawrence to use pyrex. I do things in very specific ways to minimize potential problems with the pyrex - I assume toxikon does too. If you're not very clear on those things, you could make a mistake. So I'd recommend going to a hardware store and getting a 1 gallon plastic paint mixing bucket with a 2 or 5 recycling number for your first batch, Laurence.

For one use Pyrex is ok.

I too use no. 5 or 2 plastic for everything soap related. It's cheap, light, safe and easy to use. It also comes in a huge array of sizes.

I do it occasionally too. It's not a good idea to do it all the time, but a few times isn't a big deal.

My understanding of Pyrex is that it used to be made with a better grade of glass and that is safe to use with lye. Borosilicate glass was used in the production of Pyrex, but is no longer used. Therefore, if your Pyrex is older, then it should be fine. If it is the newer soda lime glass, then continued use would be ill-advised.

See this article for more on Pyrex and when it was changed. http://www.worldkitchen.com/en/the-truth-about-pyrex-test.html

So far, the consensus seems to be that using the heat-safe plastics are a good alternative, and that for one time I should be okay with the Pyrex. I have some mixing bowls with a rubberized bottom that might be appropriate, in which case I needn't worry about the Pyrex at all. I've seen plastic suggested before too, but the source that warned about Pyrex also said that stainless steel was the safest. (I will try to dig the thread up again so that I can share it here. Maybe plastic was suggested, and I missed it?) I really don't like working with steel, though, so plastic is my preference if Pyrex isn't safe.

Pyrex does seem to be used a LOT by experienced soapers, despite the risk! I guess it's probably since it's so sturdy, and you can see everything at once. I've been cooking (not professionally) for years, and similarly I know that experienced cooks will take calculated risks that they wouldn't suggest to anyone new to the kitchen.

Earlene, unfortunately, it is all brand-new Pyrex! The old stuff seems to be indestructible. I have some glass mixing bowls and some enameled pots we got from my partner's grandmother that are at least 40 years old, and they're the toughest things. Meanwhile, my expensive new frying pans don't seem to last worth a darn. I hate to sound like a geezer, especially at my age, but it doesn't seem like stuff is built to last any more. :lolno:

alchemy_cake said:

I hate to sound like a geezer, especially at my age, but it doesn't seem like stuff is built to last any more. :lolno:

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It isn't, by and large. A consumer-driven economy doesn't work if people don't have to keep buying stuff.

Kittish said:

It isn't, by and large. A consumer-driven economy doesn't work if people don't have to keep buying stuff.

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I admit that I like to buy softer soaps because it means I get to buy more sooner!

Ok, in the spirit of informed choice, here's the Why and How.

PYREX (all upper case, usually white) is borosillicate and safe. However, pyrex (all lower case, usually red) is soda glass and risky. The problems is strength and thermal expansion. Borosillicates are strong with low thermal expansion, while soda glass is weak with high thermal expansion.

The way they make soda glass strong enough for general use is through tempering, which is a process of manipulating internal stresses on the glass via differential cooling during manufacture. But strength is predicated on the object retaining it's original shape and smooth surface. Scratches or chips will create a flaw in that surface and become an unintended focus point for those internal stresses and any others introduced by heating and cooling. I don't know if they still make them, but my high school science teacher had a demonstration that illustrated this concept very well. It was a glass bulb he would use to pound steel nails into boards without breaking, but as soon as he dropped one of those nails inside the bulb and scratched the surface, it would break. You can also observe this phenomenon in something like a glass door. A tempered glass door, when struck hard enough, will shatter completely into pebbles of glass, but an untempered door, struck much less hard, will break into jagged shards. Kitchenware isn't tempered to either of those extremes, but the effect is still in play.

So you start with a pre-stressed object and add heat. Soda glass is very mobile with temperature; it expands a lot when heated and shrinks a lot when cooled. Usually that isn't a problem if the whole item is subjected to the same temperatures. However, when there is a temperature differential among different parts of an item things can get ugly. The classic example is taking a hot item from the oven and setting it on a cold counter. The bottom touching the counter cools and compresses too much and too fast compared to the hotter parts on top and the thing shatters. A similar thing would happen if you tried heating part of a vessel over flame, or if the bottom part of a cup suddenly rose to 200F because somebody just added NaOH to the water in it. Any scratches or etchings will further concentrate those heat stresses, and you could end up with the "bombs" you see on YouTube - only this time with caustic soap solution or lye in it.

You can see why the recommendation is "Don't do it" but if you still decide you want to risk it, you must follow these cautions. 1) Never, EVER mix lye solution in soda glass. That is the worst-case scenario for all the risks of breakage and consequences if it breaks. 2) Don't microwave it. Microwave ovens by their nature encourage differential heating based on position in the box and density of the material. Heat your oils in a separate containers. 3) Keep an eye out for etchings and scratches before use. 4) Keep temperatures moderate and always be thinking about temperature differential. Don't set it on the granite countertop when it's warm, for instance.

Finally, as a slightly-off-topic aside, soda glass is also not suitable for an impromptu double boil, either. The one where you just put a bowl over a simmering pot of water. With the bottom under steam, the part contacting the pot getting full heat transfer from the metal, and the cooler top in air, that's the definition of heat stress. Soda glass can't take it reliably.

BrewerGeorge, thank you for your thorough explanation. In light of that information, I think I will wait and make sure I have safe plastic or steel to mix my lye in. I vividly remember the time I put a hot glass dish into a sink of water and had it shatter violently - I'm lucky it didn't hit my eyes, it was all over the kitchen.

As an aside, I'll be doing all of my mixing on my glass stovetop. I figure it should be able to handle the heat.

For a small batch, why not dig through your reclycle bin and see what you have in there that is big enough for your lye? I use a 32 oz yogurt container for mine (all of my batches are small). This way, you can be safe and not have to wait.

Artemis, that's a good idea. I'll see if any of my cheese containers will do. It'll just be a 1 pound batch, so the container probably doesn't need to be very big.

I also use it once in awhile for a tiny test batch. I do not mix my lye solution in pyres but will use it for a small batch of soap batter

alchemy_cake said:

Artemis, that's a good idea. I'll see if any of my cheese containers will do. It'll just be a 1 pound batch, so the container probably doesn't need to be very big.

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That's my usual batch size. The 32 oz is a nice size for that for the amount of lye and water you would use.

The rubber base on your mixing bowls might be a bit problematic if you are a messy soaper. I don't think I would survive the batter?

I don't like to use metal making soap because of DOS (even though SS should be safe) and because it's so dark in a metal pot that it's difficult to see what's happening and you can't see what's happening at the bottom at all.

alchemy_cake said:

Pyrex does seem to be used a LOT by experienced soapers,

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True. It's easier to see what's happening... especially when making transparent soap which is one of the first soaps I ever made. I melt my oils in the microwave in an 8-cup Pyrex.

toxikon said:

My comment may get some grimaces, but I use my Pyrex bowl for my oils and batter mixing. I make my lye solution in a safe plastic jug, but I do pour my lye solution into my Pyrex bowl to mix with my oils. I've been using the same Pyrex bowl for years without issue. ... It still looks brand new, I don't see any etching.

Click to expand...

^^^^^ Ditto

BrewerGeorge said:

Fully prepared for the flaming, I do exactly the same thing. I know it's not best practice and I don't recommend it for anyone else, but I feel safe enough doing it.

Click to expand...

^^^^^ Ditto.

artemis said:

For a small batch, why not dig through your reclycle bin and see what you have in there that is big enough for your lye? I use a 32 oz yogurt container for mine (all of my batches are small). This way, you can be safe and not have to wait.

Click to expand...

Good advice, Artemis. In the early days, I used 32 oz Dannon Yogurt containers. I use a re-purposed plastic lye container with straight sides and a wide mouth to mix my lye solution... set in the sink, BTW. Lye containers like the ones from WSP, Boyers, The Soap Dish, and a few others are perfect for re-use. I have several so I can make 3 batches of lye solution, stick them in the fridge to cool overnight, obviously well marked, and make 3 batches of GM soap, one after another, the next day. Works for me.

Thank you all for your advice. After all that, I came down with a horrendous cold, so I have to wait anyway as I don't want to make any mistakes due to the fatigue. Signs point to feeling better tonight, so hopefully tomorrow I will be able to post pics of my first batch!

I use Pyrex for everything! Lye, soap batter, etc! I do have one plastic bowl that I can use for lye. For soap batter, I like to heat mine in the microwave. Does anyone have any suggestions for what to use for that, so that you can see how everything is progressing? I also have used Pyrex for microwave hot process. Any suggestions there for replacements? I wonder if any plastic is see through and heat safe?