Remove all silverware from the box.
Remove the hinges to separate the lid from the main part of the box. Carefully remove any velvet or other lining material from the inside of the box.
Water a square of grass that sits in direct sunlight on a very bright day, advises Keith Husman in "Old-House Journal." Lay the curved piece of the board against the grass. Leave it outside for a day. The moisture and heat will straighten out the warp in the wood, Husman says.
Apply a coating of polyurethane over the entire box. Let it dry. This will help prevent future warping. Let it dry thoroughly in a well-ventilated area.
Reassemble the box by reattaching the hinge to the lid and box. Reattach the fabric liner if you removed it.