You just brought home this beautiful specimen, but it doesn’t look like the one you saw in the museum. Be careful—you don’t want to ruin the specimen.
Strictly speaking, once your pyrite has lost its luster, it’s hard to get it back. But here are some ways to touch it up:
1. It your specimen is covered in dirt, soak it in water for a few hours and then lightly scrub it with a toothbrush. Make sure you dry it completely afterward, or it will rust.
2. If some residual dirt is still there, you can lightly work it out with a dentist pick. This will require some patience.
3. Most pyrite is found in a limestone matrix, which will dissolve in a weak acid. Try distilled or cleaning vinegar for 30 minutes to an hour. If that doesn’t work, you can try oxalic acid, but do so carefully. Mix 1/2 lb acid in a gallon of water and submerse the specimens for 30 minutes to an hour until they achieve the desired color. Then flush thoroughly in water and dry completely.
Note: if your pyrite has a mahogany or rust-colored sheen, make sure it isn’t goethite or limonite pseudomorph. This means it isn’t pyrite anymore and will dissolve completely in acid. Use a little water and dentist tools, or leave the specimen as is.
A WORD OF SAFETY: Always add acid to water, not the other way around. Dripping water into acid can cause a reaction that will splash acid everywhere, usually in your face. Remember AAA: Always Add Acid