Stamped across refers to something that has been marked or imprinted across a surface. Antonyms for this phrase could include "undecorated," "unmarked," "uninscribed," "unstamped," "unengraved," "smooth," or "plain." These words indicate a lack of marking, rather than a visible impression. In contrast to stamped across, they suggest a surface that is clean and clear, without any distinguishing marks. These antonyms could be used to describe a surface that has not yet been marked, or one that has been intentionally left blank. Using antonyms to describe stamped across can help to create a clear contrast and make a description more specific.