stainless vs unstained

stainless is a noun but unstained is not a noun.

Word	Noun	Adjective	Verb	Adverb
stainless	Yes	Yes	No	No
unstained	No	Yes	No	No

As adjectives, stainless and unstained are synonyms defined as:

Other synonyms of stainless include unsullied, untainted, untarnished.

stainless (noun)	unstained (noun)
steel containing chromium that makes it resistant to corrosion

stainless (adjective)	unstained (adjective)
(of reputation) free from blemishes	not stained
	without soil or spot or stain
	(of reputation) free from blemishes
	not having a coating of stain or varnish