You've got a blackened stainless steel pot or pan that stayed on the hotplate too long, or perhaps a ceramic dish that was left in the oven, and the food has burned so badly that it has formed a layer of baked-on carbon gunge that you just can't get clean, even using metal scourer pads. You're thinking you might have to throw this cookware item away.
You can often salvage your seemingly ruined saucepan, frying pan, etc using the power of chemistry rather than elbow grease. I've used this method myself several times, and it really works.
- This procedure uses caustic soda, a potentially dangerous chemical that, if splashed into your eye, will quickly damage the cornea and could easily result in blindness. Wear SAFETY GLASSES or GOGGLES at all times while working with it.
- The caustic solution employed here is highly corrosive to certain metals, including aluminium, zinc, and tin. Do not use this cleaning method with aluminium or pewter vessels as it will corrode them and release flammable hydrogen gas.
- Never bring an acid of any kind into contact with strong caustic chemicals or solutions because they will react violently.
You need some crystalline sodium hydroxide, generally sold as 'caustic soda', or 'lye'. You should be able to find it in a hardware store in the household cleaning chemical section. It is typically sold in plastic jars of 500g or 1lb. Here in Australia, for example, Bunnings stores stock caustic soda.
If you can't find caustic soda or lye sold as such, in a pinch you could try Drano, which contains caustic soda along with a few other things. Unfortunately, bleach seems to be a major ingredient too, and the chlorine it releases can be corrosive to ordinary grades of stainless steel. You might end up with a dull, matt finish on the stainless surface, or possibly even rust. Keep an eye on the overall effect if you intend to use Drano. (Autosol metal polish, from an auto store, might bring the shine back if need be, but it leaves a wax film on the metal that is food-safe. I'd be inclined to strip the wax off with some kind of strong solvent and detergent.) And as for the Drano, buy the crystalline version, not the pre-mixed solution. You can then mix up a suitably strong brew.
But buy straight caustic soda if you can, and you won't have any problem with stainless steel.
Some oven cleaners contain a fair bit of caustic soda too, so if all else fails, you could try a good douse of whatever you can get along these lines.
You will also need some protective gear: eye-wear, old clothes, and rubber gloves. If you splash a tiny drop of the strong caustic solution into your eye, it could blind you. If you get it onto your skin, it will not burn like acid, but will soon begin to sting as it converts the fat within your tissues into soap. Wash any splashes off immediately with plenty of water (in which case you will feel the strange, persistent soapiness in your skin).
You will also need a wooden or plastic stirrer for dissolving the crystals. An old stick or branch from the garden should suffice.
Cover the damaged portion of your cookware vessel with cold water. Working outside or somewhere with good ventilation, and with your safety glasses in place, begin adding the caustic soda crystals to the water slowly and carefully, stirring them until they dissolve. The water will warm as the crystals dissolve, but don't let the water get so hot that it is fuming and ready to boil. There's nothing wrong with leaving some of the crystals undissolved. You're aiming for a very strong caustic solution, but you can leave the crystals to dissolve of their own accord slowly, and return later to add more if you wish.
Danger: Always add the caustic soda to the water. Never add water to the dry crystals because the heat released can cause the small amount of water to vaporise and backfire into your face.
Cover the solution and store it somewhere well away from children, animals, and potential mishaps for a few days. Check periodically (wearing your safety goggles) to stir the solution and scrape at the carbon with your stick. You should be able to gauge how the reaction is progressing. Be patient, but add more caustic soda if you think it is needed—and if the liquid will take it. If you can't coax any more crystals into solution, you've reached saturation point, and a stronger brew will not be possible.
The hydroxide ions from the caustic soda will gradually oxidise the carbon. At some point, hopefully, you will notice that the carbon has either been removed, or has been sufficiently thinned and softened so that you can easily scour the remainder away.
Wash the used solution down the drain with plenty of water. Being a simple sodium compound (and a major constituent of Drano), it is not ultimately harmful to the environment, and will not affect the sewer system any more than typical dishwashing detergents, which are laden with sodium. Seal the lid on your unused caustic soda container tightly to prevent it from attracting moisture and CO2 out of the surrounding air. Keep it stored safely for next time.
If, after several days of soaking, you find that most, but not all, of the fused-on carbon layer has been removed, you can resort to scouring the carbon away with emery paper. I have had to do this once on a particularly bad item. Emery paper is available from hardware (and auto) stores too. It's like black sandpaper for metal. Buy a sheet of medium grade and one of fine grade, and finish your work with the latter. It can be used either wet or dry (and is often called 'wet & dry' / 'wet or dry' paper for that reason). I recommend using it with plenty of water, which will keep the paper clean as you work.
Scouring with emery paper is very effective, but you'll be cutting into both the carbon and underlying metal to some extent. You'll end up with a newly polished surface on the stainless steel instead of the factory finish. In fact, if you were so inclined you could use successively finer grades of emery to produce a mirror finish and really impress your dinner guests...
The abrasive itself is not what you'd call toxic, but the adhesive used to hold it onto the paper probably wasn't formulated with food in mind, so scrub the vessel well with detergent before cooking in it again.
I make no claims as to the safety of the above. Assess this material for yourself and follow these instructions at your own risk. I stress that I am not an expert and I am not recommending anything here by implication or otherwise, except for the over-riding importance of safety. This page, like any other on the web where homespun formulations are offered, puts you, the reader, in the position of having to carefully consider and bear the attendant risks. Caustic soda is dangerous. Stay away from it or be extremely careful!