This artifact is an offset printing plate from the Washington Post newspaper.  The date of the edition is July 21^st.  Apparently this was a commemorative edition that was printed sometime after July 21^st, 1969, since the photo of Buzz Aldrin descending the ladder of the LM and the photo of the astronauts erecting the flag did not return to Earth until July 24^th, 1969.

The printing plate appears to be made of aluminum.  On it you can see the registration cutouts for aligning it on the printing press drum.  The headline for the edition is "'The Eagle Has Landed' -- Two Men Walk On The Moon."

Titles for articles include: "One Small Step For Man... Giant Leap for Mankind", "Moon Walk Yelds Data For Science", "Squared Away and in Good Shape...", "Millions Around the World Hail Lunar Landing: Follow It on TV".

The Earth To The Moon Air & Space Museum acquired this artifact through an eBay auction.