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Cast Iron Cleaning and Seasoning Help With and Tips & Techniques For Cast Iron Cookware Restoration

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  #1  
Old 08-24-2021, 01:45 PM
LVaughn LVaughn is offline
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Default Mill Scale

Can anything be done about mill scale on the cooking surface of a burned skillet?
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  #2  
Old 08-25-2021, 02:48 PM
LVaughn LVaughn is offline
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Default Re: Mill Scale

Background and Update:
I have 3 skillets (collected over time) that once cleaned presented with mill scale and the all-too-familiar orange burn marks (though this is light). They were covered with old seasoning and cooked on carbon/crud when I got them, so had obviously been used a lot since the burning. None of them are warped more than very slightly. When I saw the burn damage I just put them aside but kept thinking that they could be decent users if I could get them cleaned up and re-seasoned. I stumbled across the box with them in it a few days ago, rekindling my interest.
After posting my question a couple of days ago I read that welders sometimes use acid to remove mill scale from steel, so I decided to give it a try and gave one of the skillets a 2 hour soak in a 50% vinegar bath. When it came out I was able to rub most of the mill scale off. I'll try another soak, maybe the rest will rub off. So far I see no etching of the iron from the vinegar. Whether or not the surface under the scale will hold a seasoning remains to be seen.
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Old 09-17-2021, 03:31 PM
John_Sterling John_Sterling is offline
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Default Re: Mill Scale

If you follow what the blacksmiths do for both cleaning and seasoning (blackening and rust proofing) media blasting comes up often. I am a big fan, but I have a compressor and blasting gear. Choice of media and air pressure are critical. I use Green Diamond sand at about 75 PSI to prep all my cooking surfaces and on the big pans the bottoms as well (they get severe wear sliding on my stove). Using walnut shell media is much gentler and unlike the sand will not cut into the iron. Using soda is gentler still but at high pressure and flow will strip anything (like the paint off antique cars) with no effect on the underlying metal. CO2 blasting is the most gentle but the gear to do it is very specialized. One would want to take the pan to someplace that can do it. Many jewelers use it on jewelry with tiny rigs.

Taking the pan to any shop that can do blasting and discussing what you want is a good option and is a lot cheaper than buying all the gear. Many paint shops have blast cabinets. I would go with walnut or glass bead for starters. I have found the sand blasted surface (get no finger prints on it!) is superb for seasoning and the resulting finish is incredibly durable. But there is quite a bit to it including burnishing steps between oil coatings, etc. Not quite the thing for an antique piece intended for display although I use a special oil and everything comes out looking very good.

Edit: Black Beauty is ground slag and extremely aggressive. used to get mall scale off forgings in industry, etc. Not what to want, will chew up the underlying metal too much.

Last edited by John_Sterling; 09-17-2021 at 03:41 PM.
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Old 09-17-2021, 03:43 PM
Doug D. Doug D. is offline
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Default Re: Mill Scale

Just a reminder. There's no harm in experimenting with aggressive measures on pans already ruined by fire damage. But anything which even subtly alters the original surface texture, either as-cast or factory polished, is to be strictly avoided on intact vintage collectible pans, as it destroys collectible value.
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Old 09-17-2021, 07:57 PM
John_Sterling John_Sterling is offline
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Default Re: Mill Scale

Quote:
Originally Posted by Doug D. View Post
Just a reminder. There's no harm in experimenting with aggressive measures on pans already ruined by fire damage. But anything which even subtly alters the original surface texture, either as-cast or factory polished, is to be strictly avoided on intact vintage collectible pans, as it destroys collectible value.
An AC surface cannot be restored once it has been changed. A factory polished surface mostly can if the original method is known. The original method is simply used again. On my weird dutch oven base the sides were factory ground. This can be reproduced although I have no need to change them. I have the same grinding gear and use it. The bottom, under a thick coat of smooth carbon, revealed the marks of being smoothed with a single point tool. This could be reproduced, no matter what, in a machine shop. I only modify non-collector value stuff for my own use. If a collector wanted to buy one, or if some other piece turned out to be collector worthy, they would have to pay a good deal extra for my time and materials. These dogs are made to hunt, not show. I'd even be willing to sign the bottoms thus creating a whole new collecting niche. I wouldn't intentionally mess up something a collector might lust after to make it a better cooker for me. I'd sell it and buy a better cooker saving myself a lot of effort. At current prices I'd buy 5 better cookers.
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