Letterpress printing is a type of relief printing. This means that the image, whether it is a picture or words, is higher than the rest of the block it sits on. This image gets inked then pressed onto paper for printing. Sometimes the design of the block may be obscured by ink that was never cleaned off. It is possible to safely clean and remove this ink, making the letterpress good for printing again, or to keep as a piece of history.
Open the can of Nevr-Dull. Inside is cotton wadding polish. Tear off a bit of the wadding.
Rub the wadding over the metal image on the letterpress block. Once the wadding is dirty, replace it with a new bit of wadding.
Use a clean rag to wipe away any polish residue. This will also help determine how much more polishing the letterpress needs.
Nevr-Dull is available at many hardware and sporting goods stores.
Wooden letterpress blocks can be damaged with cleaning. If you must clean a wooden block, use a small amount of water and mild detergent and a stiff brush.