Stephen Koob is the chief conservator at The Corning Museum of Glass and is responsible for the care and preservation of the Museum’s collections.
Editor’s note: Stephen Koob works in a lab where he takes seriously all safety precautions when dealing with chemicals. Please note that we strongly recommend using the precautions noted below before using lye. Should you experience any adverse effects, please contact your local Poison Control for information.
Cleaning your beloved Pyrex — whether clear, colored, decorated, or plain — can be a challenge and should be done with care.
First, never, ever put any Pyrex through a dishwasher. This is the fastest and most damaging thing that you can do. It will slowly etch the Pyrex, and probably will not even do a decent job cleaning it. I generally recommend that you never put any glass through a dishwasher.
Second, never use any scrubbing sponge, even if it says “safe for glass,” or “non-scratch.” This includes wire wool cleaning pads.
Also avoid using sharp implements to clean off caked-on or burnt food. Glass can easily be scratched.
So, what do you use?
Start with warm or hot water and a soft sponge or cotton towel. Use a clear detergent, preferably without perfume. There are several, readily available clear detergents made for cleaning dishes. You do not need to use a green or orange detergent. The green or orange colors are dyes, and you do not need that in contact with your Pyrex. You also do not need it to smell like perfume (which is simply another chemical, of unknown type).
Wipe all the surfaces, rinse, and examine. If it is not clean, soak it in the sink or a plastic tub with hot soapy water, for an hour, or overnight. Repeat the cleaning process. If this works, rinse, gently towel-dry, and you’re done. If this doesn’t work, read on.
Cleaning stubborn stains off of Pyrex is actually simple, fast, and inexpensive, but requires some careful set-up, and some very important safety procedures. These procedures must be followed, even though my mother and most housewives from the 1950s and ‘60s used what I am going to recommend without any safety precautions. But times have changed, and there are some risk issues, and I want to protect you from those risks.
Lye
You need to use a very well-known cleaning agent, which my mother and probably most households had right under their kitchen sink. It is called “lye.” You can Google this and read up on it; it is still produced under the name of “Red Devil Lye,” or “Duda’s Red Hot Devil Lye.” Do not use oven cleaner or other materials that simply contain lye. Go to the original.
Lye is sodium hydroxide and is a very strong alkali (or base). In high concentrations, it is dangerous and can cause serious burns. In dilute (lower) concentrations it can also cause irritation and, with prolonged contact, burns.
So you need the following: rubber gloves, some plastic goggles, a plastic tub, maybe some cotton balls (or a roll of cotton), and some simple plastic brushes (a very soft toothbrush is ideal), maybe a plastic apron. Do not use natural hair brushes of any type because the lye will dissolve them. Nylon paint brushes are fine.
A Pyrex pie plate soaking in a solution of 10% lye.
Put on your gloves and goggles (and apron) before mixing. You want to use approximately a 10% solution of lye, dissolved in water. This is about two teaspoons of lye in a small juice glass (about six ounces) of water. If you have bought the liquid lye, check to see what its concentration is, and dilute it (using your favorite Pyrex glass measuring cup, of course!). If it is a 50% concentration, you can add one ounce to about four or five ounces of water. It does not have to be absolutely precise. But again, be careful. You should always add the chemical to the water and not add water to the chemical. This is true for liquid lye or crystal lye or pellets of lye. Add the lye to the water and stir until it is dissolved. This will take a few minutes; do not stand over it breathing in the fumes. You will notice that the solution gets hot. That is simply the chemical reaction of the lye mixing with the water. You do not have to use it hot, and what you do not use, you can save for later use.
Put your stained Pyrex dish in the tub. Dip your brush into the dilute lye and apply it to the stains on the Pyrex. Light stains will almost instantly dissolve, evidenced by brownish drips down the side. Heavier stains, such as caked-on casserole, burnt meat, or pie crust may require a second or third application. In between every cleaning, lift the Pyrex dish out of the plastic tub and rinse it with warm water. This way you can evaluate the cleaning process. You rarely need to have the lye on the dish for more than 20 to 30 seconds.
-
- Pyrex surface before cleaning.
-
- Pyrex surface after cleaning.
Deep, serious cleaning may require some soaking or cotton compresses, wetted with the lye solution. In general, these stains get trapped in the “PYREX” lettering on the bottom of the glass pie dish or Pyrex bowl, on the scallops of a pie dish, or the edges of a bowl or casserole rim. Again, this cleaning should always be done in the plastic tub, gently pouring the lye solution onto the cotton or around the rim (of a pie plate or casserole dish). Leave it on for two to three minutes, remove and brush as before, rinse. Repeat, if necessary.
-
- Edge of handle before cleaning.
-
- Edge of handle after cleaning.
I have yet to see a stain or food residue that this did not work on, and I have never seen the lye change the color of a Pyrex dish, or damage the glass. It will reveal if the glass has been over-cleaned, because, once you get all the stains off, scratches and damage from previous cleaning will be easy to see.
Rinse your Pyrex dish at the end. Towel dry with a soft cotton towel. Rinse your gloves, tub, brushes, etc., and store them away for next time. Save the diluted lye in a plastic bottle. Label it and keep it out of children’s reach.
Damaged Pyrex, primarily from over-cleaning, cannot be fixed. There is no way to safely re-polish Pyrex, or recoat it.
Final precautions
- If by accident you spill some lye on your clothes, shoes, or bare skin, rinse it off immediately with water.
- Avoid getting lye on anything wooden or aluminum. It will darken (burn) wood, and slightly etch aluminum.
- Avoid breathing the fumes. This is why lye was generally discontinued as an oven cleaner. It’s as bad as getting a whiff of ammonia.
- If you would prefer to dispose of the diluted lye, we recommend contacting your local water treatment plant or waste management company for instructions on disposing of hazardous materials.
Will the lye method work on ground stoppers that seem permanently stuck to the bottle?
From Stephen Koob: Having a ground stopper stuck in a bottle is one of the most difficult challenges to solve. Usually the issue is how much force was used to put the stopper in, but it can also be what the contents of the bottle are. If it is an alcohol, it may also have sugar, if it is a perfume, it may have flower extracts. Not all of these would be affected by lye, but it is certainly worth a try. The biggest problem is getting any kind of solution to go into the stuck stopper. Usually it just sits on the surface,
I usually try, in this order: water, alcohol, acetone, naphtha. Warm water, hot water. Careful tapping with a wooden spoon. Many times we have been unable to remove a stopper, but 9 times out of ten one of these methods works.
THANKS! I will try what he says.
I know this question was a year ago but anyway…. When I was a kid I had been mucking around with one of these bottles and then couldnt get the stopper out for love nor money. My father (a pharmacist) carefully warmed the bottle and simply removed the stopper. Turns out air pressure has some serious grunt!
My husband thinks it’s ok to cut directly into foods in pyrex with a knife because he’s never heard it wasn’t. Could someone explicitly say that it isn’t? I’d assume not since even scrubbing pads can damage them.
Hi Laura – This is from our conservator:
Yes, there are several issues with cutting food directly in a Pyrex dish:
1) this will scratch the Pyrex, and eventually, the glass will end up looking like a cutting board (heavily scratched). This is worse for clear glass than white or colored Pyrex.
2) this will dull your knife faster than using a cutting board.
3) there is a very small risk the scratches could make the Pyrex more at risk to cracking from rapid heating or cooling.
I would discourage it, if at all possible.
Stephen Koob
I used all my lye solution. all that is left is the waste in the plastic tub. Can i safely dilute this and toss into my rock landscaping
Hi Tina – Our conservator, Stephen Koob, says yes.
Is it possible to email Stephen Koob directly? Is it possible to email directly any staff member of cmog? But here is my comment-
I have been easily removing tough black baked on grease off of old clear and colored Pyrex for years using Oven Off, or any spray type oven cleaner, works great. I’m sure others do the same, much better than the elaborate multi-step lye cleaning process! I have never noticed any damage to clear Pyrex or especially to the gloss/enamel of colored Pyrex, no damage, nothing. I wonder if you cleaned baked on grease off of any Pyrex item 100 times with just spray on oven cleaner, would it still do no damage? In order for anything to damage anything, or remove anything, there has to be just the right specific chemical reaction. It seems there is no damaging chemical reaction in the case of using spray on oven cleaner to quickly and easily remove baked on grease off any old Pyrex. This is much preferable to the long multi-step lye cleaning process, or am I wrong???
Hi Richard – We don’t share the personal work emails of staff for many reasons. But this page: https://www.cmog.org/collection/conservation has a link to a form in the right-hand column that may be useful.
But please know that I forwarded your question to Steve Koob. He’s pretty good about answering but sometimes it takes him a couple of days. So stay tuned …
Hi Richard – Here is your answer from Stephen Koob:
Most oven cleaners are just lye, or at least used to be. So it’s the same material.
I don’t understand what the “multi-step” issue with using lye is about. Once you have the solution, you apply it and rinse it off. Just takes seconds.
Whether you use oven cleaner or lye from solution, thorough rinsing is important, and of course, wear gloves. Oven cleaner based on lye will burn your hands too.
Keeping a chicken warm in the oven in a Pyrex dish covered in foil has discolored the colored exterior of the dish where the foil overlapped it. The white rim and interior are not stained. I think it must have been a chemical reaction of the foil with the glaze. Barkeepers Friend has no effect on the stain. Do you think lye will take it off?
0503 . Part of a set, wedding gift 1968:
Hi Karen – This is from our conservator:
I have never seen this happen and we do a lot of cooking with foil wrapped around the Pyrex.
How old is the Pyrex ? Corning stopped making Pyrex in 1995, and since then the manufacturer may have changed the colors and surface applications—you would have to check from where it was bought.
I would try some lye on one small are, rinse and see if there is an improvement. Otherwise, I do not know of any way to remove aluminum residues (if it was aluminum foil).
Thank you both. There was no pure lye at the grocery store, so we settled for drain-cleaner crystals (which probably horrifies you — sorry.) It took a half-hour of soaking, but the stains are gone! We’re relieved. This dish is the largest of a four-dish lidded set that was given to us as a wedding present fifty years ago, and we didn’t like to see it discolored. These are not collectibles to us, they are essentials! Like our many Corningware wedding gifts, they began to get much more use when the microwave came along. I must admit that they’ve been through the dishwasher hundreds of times, which may have made the 1968 surface more susceptible to stains.
Thanks again for your advice and for this website.
You are absolutely right. I had my pink Pyrex for 12 years and tonight I made scallop potatoes and had aluminum foil over it for the first time! Absolutely the first time it has stained since I usually only use it for bars! Lots of hard work to clean it and now am soaking it again in water and soap detergent.
got it! Yippee. Got it for pinkish color Pyrex. Used Oxi Clean laurndry spray and it added oxygen it oxyidizing it and came out perfect. Didn’t even scrub it. Used my fingers. Can’t believe it. Not sure if that would work on the other colors. It was the foil that changed the color!
Will this method work for non grease or baked on food issues such as black marks on outside of casseroles. Assume stacked with pots and pans. Thanks.
Hi Jan – This is from our conservator: All I can say is “not necessarily,” depending on what the mark is. It will probably remove some, but not all. Certainly worth a try.
I have an Aladdin lamp chimney made by Pyrex from 1954 to 1960. It had a tenacious residue on the inside. I tried numerous cleaners and then stumbled on to this blog. Sodium hydroxide did the trick. I stood the chimney up in a cut off two litre bottle and poured in the solution. Now the bottom is spotless and the top still looks bad as it was not soaked in the solution. The problem is that I don’t want to harm the Pyrex label at the top of the chimney because there doesn’t seem to be many of them around that were made by Pyrex. Will the label withstand the sodium hydroxide? Is the label etched or lithographed?
Hi Mark – This is from Stephen Koob, our conservator: I am not familiar with Pyrex labels. Is it paper, or etched into the glass? Perhaps our Rakow Research Library can help. Etched surfaces can be safely cleaned using sodium hydroxide, but NOT paper.
No it’s definitely not paper. My best guess is that it’s etched but it seems to have a greenish tint to it. Perhaps the green is dirt, but I fear it may be a lithographed or stamped paint. I will get some thicker glasses and a magnifier. To bad I can’t send a pic, I’ll check out the Library.
As it turned out, the label was etched and my Pyrex chimney is absolutely spotless. The extrusion ribs are now well defined and the tenacious residue is completely gone. DRANO® KITCHEN GRANULES were the closest thing I could find to pure Sodium Hydroxide. According to the SC Johnson spec sheet it’s somewhere between 60 to 90 percent pure. The remainder is Sodium Chloride. I got it at Shop Rite and it worked very well. Thank you!
Great info! Paranoid about trying this with the gold-toned decoration on a Starburst Cinderella casserole dish. It’s also a “peach” test color variant, which I didn’t see listed here on the site, although black was. 😊
I used a cooking bag in my clear glass rectangle Pyrex. Now there is a film on the glass that must have come from the cooking bag . Any suggestions on how to remove it?
Hi Shel – This is from our conservator: I am afraid I do not have an answer to this. You should check with the manufacturer of the cooking bag. It must be some plastic residue, and without knowing the plastic, we cannot guess what would remove it.
My pyrex was packed using packing paper for dishes. Put in box with other dishes. Stored in a warehouse for 1 month. Today I unpacked it. The Daisy orange/ yellow is stained with something. The Chartreuse and red too. Any ideas on how to clean them. We use these regularly. Thank you
I have some vintage Pyrex flamingo pink plates, bowls, etc. the pink portion has a cloudy film on it. when I run water over the dishes, the pink looks bright but when they dry, it has a white film on it. Any ideas on how to remove the white cloudy film? Thanks!
Is there a way to restore the shine to the painted surface? I have two verde Cinderella bowls that have gone matte. My though was auto clearcoat on just the outside and then handwash only.