7 Antiques You Should Never Clean (Unless You Like Losing Money)

Why cleaning ruins value: Rubbing, dipping, or polishing strips away original luster and microscopic texture known as the coin’s “skin.” Once that natural finish is altered, major grading services like NGC label it “Improperly Cleaned,” which means it can no longer receive a numeric grade and usually sells for significantly less than an uncleaned example. This will make selling that old coin collection you inherited significantly less enjoyable.

What to do instead: Handle coins by the edges and blow away dust with a rubber bulb. If you see green residue or tackiness from old plastic holders, take it to a professional conservator.

Never do: Toothpaste, baking soda, jewelry cloths, or chemical dips

Why cleaning ruins value: Over-polishing the metal softens crisp case edges and can eventually erase the original brushing that collectors seek out. Even a light dial cleaning done incorrectly can remove logos or patina that mark a watch’s authenticity.¹

What to do instead: Wipe the case gently with a microfiber cloth. For servicing, tell your watchmaker “no polish, no redial” in writing.

Never do: Buffing wheels, metal polishes, or DIY dial cleaning

Why cleaning ruins value: Bronze develops a natural patina over decades that signals age and authenticity. Harsh cleaners or scrubbing remove this finish and leave a patchy, unnatural shine.

What to do instead: Dust with a soft brush. If you must remove fingerprints, use a barely damp microfiber cloth and dry immediately.

Never do: Brasso, ammonia, acids, or steel wool

Note: Unfortunately, reproductions of 19th-century bronzes, including those signed by artists like Auguste Moreau, are common. These copies often miss the fine casting detail and patina of originals.

Why cleaning ruins value: Tin litho finishes are thin and delicate. Solvents or even water can lift ink or damage decals, and “touch-ups” are easy to spot and hard to undo. Once the finish of a metal toy is lifted or dulled due to cleaning damage, the value can be cut in half.

What to do instead: Use a soft artist’s brush to remove dust. For sticky spots, barely dampen a cotton swab and stop immediately if color transfers.

Never do: Magic erasers, detergent, or overpainting

Why cleaning ruins value: Acidic cleaners or abrasive pads dull the glossy enamel and make chips spread. Collectors prefer signs with natural wear, not a polished-down look.

What to do instead: Wipe gently with mild soap and water, then dry by hand. If you want shine, use a non-yellowing museum wax sparingly.

Never do: Bleach, ammonia, scouring pads, or paste polish.

Why cleaning ruins value: Even light wiping can strip away centuries-old varnish or disturb the paint layer beneath. Overzealous cleaning and amateur varnish removal have permanently dulled countless works of art that once had rich surface depth and tone.

What to do instead: Dust gently with a soft brush or microfiber cloth, avoiding direct pressure on the canvas. If a painting looks dark or cloudy, consult a professional conservator who can safely remove surface grime or revarnish without harming the original pigments.

Never do: Use water, soap, or solvents

Why cleaning ruins value: Water and heat can blacken or lift the foil beneath antique gems on Victorian and Georgian jewelry, which could essentially destroy the piece. Once damaged, the look is almost impossible to restore, and the value is significantly reduced.

What to do instead: Gently wipe with a soft dry cloth. For loose settings, ask a jeweler who specializes in antique pieces.

Never do: Soaking, steam, or ultrasonic cleaning