Cast iron weirdness

We had three cast iron pans from a thrift store. Not knowing their history, it was suggested they be put in the oven for a cleaning cycle to eliminate as much uncertainty from their past as possible. Two of them have "Kirby & Allen" imprinted on the bottom, the third says nothing. They went in looking normal and black, but came out like below. Any conjecture as to what happened?

Wow, that IS weird if the two white ones were black originally! They look like half-worn-off white enamel to me.

It is white and dusty, but after rubbing at it with my fingers, they get white and the pans stay white underneath. A DDG search turns up info about calcium/mineral deposits making white spots on cast iron, but nothing that mentions the whole thing turning white from high heat.

This link is for rusty cast iron.. but vinegar was my intuitive answer. Maybe steel wool, or even a wire wheel on an angle grinder. (Dust mask/respirator just in case?)

https://southerncastiron.com/how-to-fix-rusty-cast-iron/

Maybe they were not seasoned, but painted or coated with something else just for looks as an "antique?"

Are the two Kirby & Allen the ones that turned white?

Mercy Pergande wrote:Are the two Kirby & Allen the ones that turned white?

Yes. The one that stayed black has no identifying marks. Searching online it seems likely the K&A are of Asian origin, where they've been known to emboss pans with Western sounding names for sale abroad. I wouldn't think they were trying to make them look like antiques, but rather to find a cheap way to season and/or protect them from rust...?

Is there any chance they are cast or anodized aluminum?
I had only ever seen aluminum get that white cast and the oven temp would have been super high for aluminum which would also possibly add a white ashy cast.
You could still re-season them at a lower temp and they would be great heat conductors and light weight!

I can only think that previous owners tried to use oven cleaner or some other type of cleaner that they didn't remove thoroughly. If the white is dusty and you're able to remove a bit of it, try scrubbing a small portion of one of the pans with fine steel wool and a mild dish detergent. You may be able to remove the white residue that way.

A brief online search on cleaning vintage cast iron calls up millions of sites, but this is the best of the 1st-page results: https://www.castironcollector.com/cleaning.php  In it, the author does not recommend using a self-cleaning oven to clean vintage pieces. He suggests that the super-high heat of modern ovens is a bit more than the older iron pots can take without warping. That makes sense to me.  This seems to be a pretty good site with lots of resources.  The CastIronCollector site also has a forum on Kirby & Allen pans https://www.castironcollector.com/forum/threads/kirby-allen.1505/

I love my cast iron fry pans and braisers, although a long-cooking tomato-based sauce will ruin the top edge finish on a cast iron pot. Ask me how I know (sigh.)

This site,  https://fieldcompany.com/pages/a-visual-guide-to-caring-for-cast-iron suggests that the cause is due to a build-up of oils in a vain attempt to season the pan. I know that I have been guilty of trying to "hurry the seasoning" along and ending up with a gummy mess in my favorite pan.  Keep at it.

Barbara Manning wrote:the author does not recommend using a self-cleaning oven to clean vintage pieces. He suggests that the super-high heat of modern ovens is a bit more than the older iron pots can take without warping. That makes sense to me.  This seems to be a pretty good site with lots of resources.  The CastIronCollector site also has a forum on Kirby & Allen pans https://www.castironcollector.com/forum/threads/kirby-allen.1505/

Not a forum, a single thread where they indicate this is probably an example of common marketing strategies from Asian producers. Given some of the stuff that has escaped the Asian export market in past products, I'm willing to keep poking around a bit more before proceeding with a recovery strategy.

It doesn't seem likely a product of gradual seasoning attempts, it is uniform around the entire surface as if it were dipped or sprayed with something. The pans are of a comparable stature to regular Lodge pans, hefty and plenty thick walled to have withstood the temperatures of the Self Cleaning Oven already.

Full disclosure: These pans were found deep in the annals of the Duke Cave here at the labs, behind one of the discarded Arks of the Covenant lying around. The arcane price tag around the 3 handles read $19.95, though the provenience of the purchase era has not been determined so it cannot be translated into contemporary economic terms precisely. We want to be sure these are free of gick before risking exposure to the boots, and the Duke himself advised that the oven was about due for cleaning anyway. Plenty of other projects to tackle and larger casties in service already here, these would just be an added convenience if the chemical riddle reaches a satisfactory explanation...

Here's the collective wisdom on cast iron from over at richsoil: https://richsoil.com/cast-iron.jsp There is a blurb in there on using a self cleaning oven.

I'm thinking the white stuff is a bunch of ash. I'll try some wet scrubbing tomorrow to see if it enough comes off to look like raw iron...

For what it's worth you'd be able to tell whether it's aluminum or not by comparing weight of similar sized cast iron pans.

aluminum is something like half the weight of iron.

There's also the magnet test....

Coydon said, "I'm thinking the white stuff is a bunch of ash. I'll try some wet scrubbing tomorrow to see if it enough comes off to look like raw iron...

I am really curious to see this happen.

Does it look like metal turned white or more like porcelain?

If it happens to be a porcelain coating it could be dangerous to sand it as it is like glass.

I'm fascinated by this- I have spent the better part of last night and today trying to figure out what might have caused the white cast on these pans (I like research and I'm a creative hunter so I enjoyed the challenge) and was kind of amazed at being unable to find a satisfying solution.

My best guess is that it is some kind of ash but my (lack of) understanding of metallurgy didn't tell me if it was something that would have been from the manufacturing process or if contaminants would have certainly burned off during casting - I believe that is the case and found no dependable information that cast iron varies much in composition based on place of manufacture. i learned that there are 4 types or grades of cast iron - gray, white, ductile, and malleable, but again without understanding metallurgy, I wasn't able to connect any to cookware or this specific issue.

I did see that calcium, magnesium, and silicone were known to leave white ash within a self cleaning oven. I wondered if the pans had been coated in something silicone based to "pre-season" them.

I also noted that some cast iron was coated with some type of thin enamel (not like a true enamel coating which is sturdy and heat proof) which i could imagine, if it was already fractured due to wear and tear, could have powdered completely under that kind of  heat.

"Overfiring wood stoves" was a topic I dug into after seeing that it cause cast iron stoves to turn white. No satisfactory connection to the skillets, but interesting at how very white the iron became.

I don't know though. It's amazing how much repetitive info there is online about cast iron, and not much else. I'm continuing to read what others come up with interest!

I may be offside, but unless they are family heirlooms I would be tempted to put them in a giant pot and boil the hell out of them. If it's some sort of cleaner or other substance, that should soften it and pull the gunk out of the pores and into the water, or at least make it scrubbable. My 2c.

If they are indeed cast iron (and as L. Johnson says, you should be able to tell from their weight), my best guess is that it is ash. I have had seasoned cast iron turn white when exposed to a really hot fire - it burned off all of the oil and food reside and turned it to ash.

If the weight/magnet tests fail then my best guess is that it is magnesium or aluminium. Aluminium oxidises to form a white powder which you may have seen on old cookware, window frames or door furniture.

I have vintage Le Crueset pans which are cast iron with an enamel coating. The enamel is thick and I can't imagine how it would burn off in a domestic oven - I imagine you'd need a pottery kiln to touch it.

It's worth noting that metals can be pretty bad for your health and it would be worth wearing a respirator or mask when removing the white powder. Cast iron is fairly inert, although I wouldn't want to ingest large amounts of that either!

I wouldn't worry over it; I'd just throw those things away.

Luke Mitchell wrote:

I have vintage Le Crueset pans which are cast iron with an enamel coating. The enamel is thick and I can't imagine how it would burn off in a domestic oven - I imagine you'd need a pottery kiln to touch it.

To clarify, I was referring to a thin powder coat or something like an enamel paint to give it a smooth surface, like a light spatterware, than proper enamel like LC
However, you are probably correct that that isn't the issue because we have all seen old enamelware coffee pots sitting over a campfire and doing just fine.

I thought like Mercy. Clearly it's not a true enamel coating, but some sort of cheap alternative that's burned to the white dusty stuff.

Coydon Wallham wrote:
I'm thinking the white stuff is a bunch of ash. I'll try some wet scrubbing tomorrow to see if it enough comes off to look like raw iron...

Since the pan that didn't turn white seemed normal enough to cover in bacon grease and start using, I met my main goal of putting a medium cast iron into the rotation here with all of the large ones and the weird ones got 'put on the back burner' for a bit.

Both rubbing with a wet towel and scrubbing with 0000 steel wool made the white ones look close to raw iron as I could tell. However, once the moisture from the towel evaporated, that area looked white and chalky again. The area scrubbed with steel wool started grey and developed a light patina of rust over the following days. This fit with what I would expect from having successfully removed whatever had been on it previously.

Today I resanded one entire pan and rubbed bacon grease over it. The only problem is the bottom has elaborate rings cast into it. Besides making it very difficult to scrub off by hand, it would be an inefficient pan to use on the glass stove top here. Being the same size as the previous one it is superfluous and doesn't seem worth the time to finish.

For the sake of future efforts, is it okay to coat the outside/bottom of pans with bacon grease also? I've always just had to deal with the interior and kept the factory seasoning on the outside, not sure if bacon grease out there would cause a mess...?

It will likely work fine on the glass top stove, as I believe the ones I've seen use radiant heat more than conduction. Having liquid oil/grease on the outside will generally burn and smoke and make a mess, but if it's been seasoned and is solid, not so much. But the normal course of cooking will generally get some stuff on the stovetop anyway, so it may not be a big deal to you.