Instructions
Identify a butter knife by its shape. Look for a comparatively blunt, wide, cutlass-shaped blade terminating in a rising point. Cheese knives share a similar distinctive form, but are usually thinner with a forked point and a serrated bottom edge.
Establish whether the butter knife is sterling silver by examining it for hallmarks. If you see the words "Sterling" or "Sterling silver," then the butter knife is definitely silver, and probably American with a date from before 1900 -- in other words, undoubtedly an antique. A numerical standard mark -- "925" --- as well as or instead of these marks would also suggest that the piece is American, but of 20th century vintage. For other marks, continue on to Step 3.
Look for an emblem of a lion walking sideways. This is the "lion passant," the silver standard mark of British silver. Silver from Great Britain also comes with date letter and assay office marks which will enable you to find out precisely when and where your butter knife was hallmarked -- in other words, whether or not it is antique. Other useful silver standard marks to look out for are the kokoshnik, a woman in a headdress, on Russian sterling and the Minerva, a classical female profile, on French examples.