Cleaning Copper Cookware
Thanks in advance for all of your helpful insights.
I have recently purchased some copper cookware that has scarcely been cleaned. It is a four piece set (not including the lids) made by Bourgeat. It is high quality (2.5 mm copper, lined with stainless steal, iron handles).
The original owner used them a lot, but never cleaned them. There are two forms of mire on these pots.
The first form is the typical oxidation byproducts from normal heating of copper, which has caused the pots to discolor. Some affectionately call this "patina," and many don't mind it. My preference it to keep my pots shiny, so I routinely clean this patina off of my other copper cookware with lots of paste formed out of powdered "Barkeeper's friend" and even more elbow grease. I don't mind this effort, and consider it the 'cost of doing business' when it comes to cooking with copper.
The second form of damage is the reason I am writing, and the likes of which I don't know how to effectively attack. What I am referring to are dark black stains of burned on oil and grease. These do not seem to be removed by Barkeeper's friend, no matter how hard I scrub.
The attached photos show the bottom of my frying pan, which has been cleaned with Barkeeper's friend. The "patina" has been removed, so the copper is bright and shiny, but the black stains remain. Another photo shows the side of the pan, which I have not cleaned yet, simply to demonstrate the state of the pan before my attempts to clean it. Near the handle, you can see the built-up black crusty deposits, though most of the black stains on the rest of the pan are flat, not raised or crusty.
When my enameled cast iron cookware (Le Creuset, Staub) gets these burned grease marks, I spray it with oven cleaner about once a year and let it sit for a day. Oven cleaner is essentially an extremely strong base (like high concentration sodium hydroxide). However, the oven cleaner specifically says "not for use on copper."
I am confident the oven cleaner will remove the burned-on grease from my copper cookware as it would from my enameled cast iron, but I don't want to ruin copper cookware that I can barely afford used, let alone new.
Will oven cleaner permanently damage the copper?
Will other chemical cleaners of copper be useful for this burned on grease? Some have recommended the following list of cleaners, but I don't know if any of them can tackle the burned-on grease marks:
Flitz Metal Polish
Am I stuck having to ship these to a copper cookware re-tinner to professionally buff the exterior of the cookware, or are there other metalworking shops that can easily and cheaply buff them?
Any and all suggestions are most welcome! Thanks again in advance for your efforts in helping me.
First of all, retinning does not apply in this case since the interior surface is stainless steel.
400 grit autobody sandpaper will remove the grunge. 2000 grit will polish away all the scratches left behind by the 400 grit and bring the exterior to a very, very high shine. It'll look like brand new. You might want to buy some 800 or 1000 grit and progress through the grits up to the 2000 grit. AutoZone carries these papers - wet/dry paper. Use the 400 dry but wet the higher grits with water as you move up to finer and finer grits. Stay with the 400 grit until the grunge is completely gone.
I wouldn't use a chemical product on the copper, just sand them out and keep them cleaner in the future.
FWIW, Barkeeper's Friend is an abrasive, basically just loose grit (rottenstone) unadhered to sandpaper. It would be equivalent to about 800 to 1000 grit autobody sandpaper although the mineral compositions are different. Rottenstone is also used in furntiure finishing to rub out varnish and lacquer.
Those are heavily greased pans. You can try basic solution like thick baking soda solution to remove burned grease, but it may not able to clean it to the original shine. At the end, you will probably have to mechanically sand it out. The problem is that you are thinning your copper, everytime you sand/buff it.
Sandpaper (fine grit) and elbow grease will do the trick. Best is the aluminum oxide 'wet' paper. Then some form of scouring powder to buff out the scratches from the sandpaper.
FYI: If you regularly polish your copper, it will get thinner over time. Can't help it, each polishing will remove maybe one or two thousandths of a millimeter. That means after 3 to 5 years, your 2.5mm copper will be 1.5mm copper.
I think this may be your best bet. Anything that can have the ability to etch the copper will result in an uneven finish since it will eat the exposed copper and thinner layers of crud first. I would look for 320 grit or higher, automotive finishing sandpaper as suggested above.
Here's what I'd do ... And we're talking about the BOTTOM EXTERIOR of the pans, right???
Go to the hardware store and buy yourself some bags of plain steel wool pads. Go with Grades 0, 00, 000 and 0000. When you get home, start with the finest (0000) and work at it for awhile. Don't be stingy with the pads. If it doesn't cut it, fist try adding in a little Bon Ami powder, Goddard's copper polish or Copperbrill, then step up to the next coarser grade (000). Use the finest grade that actually cuts the crud. After you get it off, work your way back DOWN to the finest again. In working your way back down, you want to polish in a straight line; when you change grades, you polish in a perpendicular direction until all previous (coarser) marks are gone. After you finish with 0000 grade, if you want a mirror finish, take the pan to a local machine shop, and tell them you want the exterior LIGHTLY buffed on a fresh sewn muslin wheel at 1750 RPM using "white chrome" rouge. This is what the retinners use, except some of them use a bigger badder buffer called a saddle buffer.
Hope this helps. If you want to send it out, the best is Peter at Rocky Mountain Retinning in Denver (a lot of others will lie to you and send it to Peter themselves!)
Oh, and I'd leave the chemical and thermal stripping to the pros.
I use Easy-off oven cleaner to get the varnish and black crud off copper pans and I find nothing on the label that says not to. If you warm up the pan a bit it does the job in 3-5 minutes and does no visible damage to the pan. The label does recommend against using on enamel and aluminum (try that sometime when you don't want to use your aluminum pan ever again), but there is no mention at all of copper, pro or con.
As for sandpaper or other abrasives, if they are fine enough not to scratch the surface they won't do a good job of removing the crud, and if they are coarse enough to remove the crud they will scratch the copper.
I remember seeing something in an old-fashioned catalog once (The Vermont Country Store maybe?) which was some sort of solvent sold to remove baked and burned discoloration on cookware. I wish I could be more specific, but I know that what you are searching for does exist...
This might be what I'm thinking of --