How do I stop an iron meteorite from rusting?
Keep it as dry as possible with silica gel in an airtight container, handle it with gloves, never wash it in water, and, for cut and polished pieces, consider a thin protective coating; persistent rust may need advice from a specialist.
Iron meteorites are made mostly of iron-nickel metal, which rusts in moist air just as a bicycle chain does. Some are particularly troublesome because they contain small amounts of chlorine, picked up while lying in the ground. Chlorine combines with iron and water to form corrosive compounds, sometimes called lawrencite, that can keep a specimen "sweating" droplets of rusty liquid and slowly crumbling. Once this process starts, it can continue even in fairly dry air, so prevention is far easier than cure.
The first rule is dryness. Store iron meteorites in an airtight box or cabinet with plenty of fresh silica gel, and keep the relative humidity low; many collectors aim for below about 40%. A small humidity gauge inside the box is a useful check. Avoid places where temperature changes cause condensation.
The second rule is minimal handling. Sweat and skin oils leave salty fingerprints that rust readily, especially on polished surfaces. Wear nitrile or cotton gloves, and never wash an iron meteorite in water.
Cut, polished or etched slices are the most vulnerable, because their bare metal is exposed. Collectors often protect them with a very thin coat of a conservation wax or a light oil, applied sparingly and reapplied over time. Thicker lacquers can trap moisture underneath, so less is more. If rust appears, act early. Light surface rust can sometimes be gently removed with a soft brush, followed by careful drying. Some collectors use pure alcohol to drive out moisture, which is better than water, though it should be used only by adults with good ventilation and no naked flames. Do not use acids, harsh chemicals or heat to remove rust: they can damage the meteorite and are unsafe, especially for children. For badly affected or valuable specimens, ask a museum conservator or experienced dealer for advice.