Remove as much furniture as possible from the room when painting ceiling tiles in place, and cover the remaining furniture and the floors with plastic sheeting and drop cloths.
Wash the ceiling tiles with a rag, hot water and grease-cutting detergent. For very heavily soiled tiles, use tri-sodium phosphate cleaner; for lightly soiled tiles, dishwashing detergent will work just fine.
Remove loose rust and paint with sandpaper. If the tiles are heavily embossed or stamped, use steel or copper wool. Wipe them down with a damp rag.
Prime the tiles with shellac- or oil-based rust-inhibiting primer. Use a sponge or lambswool roller to more easily paint a stamped surface. If you're just painting a few tiles not installed on a ceiling, use a paintbrush. Allow the primer to dry as indicated on the can.
Paint the ceiling tiles with two coats of water-based paint. Antique stamped tiles look better in a satin or semi-gloss finish because it highlights the decorative texture.