[The Saucepan Man]

Now that is just a common, widespread proverb, so you can't say Tolkien quoted Shakespeare when he used it!

I'm not saying that Shakespeare didn't nick it himself.

Courtesy of Google:

"All that glitters is not gold" is from Parabolae, a book of poems written circa 1175 by Alanus de Insulis, a French monk: Non teneas aurum totum quod splendet ut aurum = "Do not hold as gold all that shines like gold". It was Englished [sic] by Chaucer in The Canterbury Tales (1389) as: "But al thyng which that shyneth as the gold /Nis nat gold, as that I have herd it told." (Shakespeare used the wording "All that glisters is not gold" in The Merchant of Venice; "glister", an archaic variant of "glisten", is still sometimes heard in allusion to this.)