Here's all that TTi has to say...some applies to chrome or stainless... Fast Orange hand cleaner has worked well for me in other applications.
After Header Installation and Before Engine Run - Remove grease and/or skin oils from the header tube surface. Stains & fingerprints will show when header gets hot.
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Nickel Chrome Plated Headers: Wipe down tubes with rubbing alcohol and a soft cloth, dry thoroughly.
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Ceramic Coated / Polished Ceramic Coated Headers / Stainless: Wipe the tubes down with an environmentally safe Orange Cleaner Degreaser or mild soap, warm water and a soft cloth, dry thoroughly.
When storing your car for an extended period of time, some precautions must be taken. Park the car over a large sheet of plastic or tarp. This will protect your car and headers from moisture seeping up through the floor. Wipe down and dry the headers thoroughly. Then coat the headers with WD-40 or an equivalent where the tubes are welded to the header flanges and where the tubes come in close proximity to each other (especially where the four tubes enter into the collector). These areas are prone to rusting, as the coating is unable to get between the tubes in the unexposed areas of the header. If rust occurs, it will travel into and under the coating and create a stain. When you are ready to start the car after storage, wash the WD-40 off by following the cleaning procedures.
Cleaning: Road grime / Oil / Grease / Surface deposits (surface rust) from water or other liquids
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Use an environmentally safe Orange Cleaner Degreaser, warm water and a soft cloth. Two or Three cleanings may be required. Be sure to dry thoroughly.
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Use cleaning compounds like, Nevr-Dull, Mothers or Wax Shop and about 15-20 minutes of elbow grease.
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Stainless Steel: Nevr-Dull Wadding Polish
Polish to Revitalize Coating
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Nickel Chrome Plating: Bluing / discoloration is inevitable. You cannot remove it, although there are products that claim to do so like, Blue-Job Chrome Restorer.
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Ceramic Coated / Polished Ceramic Coated: Mothers PowerMetal or Nevr-Dull.
For More Aggressive Cleaning: Stains / Baked-on Oils or Fluids / Melted-on Microfiber Towels or Plastic Grocery Bags (Yes, this happens a lot)
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Try a Super-fine "0000" Steel wool pad or use an Ultra-fine Scotch-brite pad.
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If all else fails, spray paint! Use Krylon 1402 High Heat Spray Paint – Aluminum color. Once headers heat up, color will or should blend.
Unfortunately, you cannot bring back a “High Luster” Polish (“C5” coating option) appearance.