Each day in June you'll get an entry showing you the first appearance of seemingly minor characters, phrases, objects or events that later became notable parts of comic book lore. Not major stuff like "the first appearance of Superman," but rather, "the first time someone said, 'Avengers Assemble!'" or "the first appearance of Batman's giant penny" or "the first appearance of Alfred Pennyworth" or "the first time Spider-Man's face was shown half-Spidey/half-Peter." Stuff like that. Here is an archive of what I've featured so far.
Today is an all-metal edition!!
Enjoy!
Reader Glenn S. wanted to see the first of the fictional metal Adamantium and he also wanted to see the first time it was revealed that Captain America's shield was made from Adamantium and Vibranium. Can do, Glenn!
First appearance of vibranium
In 1966's Fantastic Four #53, we were introduced to vibranium (this was also the introduction of the villian, Klaw)...
Interestingly enough, Stan Lee also introduced a DIFFERENT vibrating metal just a few months earlier in Daredevil #13....
This metal has retroactively been termed Vibranium, as well, just the Savage Land version of the metal.
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First appearance of Adamantium
In 1969's Avengers #66, we got our first look at adamantium and its creator, Dr. Myron MacLain...
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First mention of Captain America's shield as an adamantium/vibranium alloy
In 1981's Captain America #255, we learn that Cap's shield was the result of a metullurgical accident...
In 1985's Captain America #303, we meet MacLain again, who, we learn, created Captain America's shield...
He later explains how the shield came about...
And yes, as noted in the comments, the mixture is not precisely adamantium/vibranium. It is steel plus a "mystery something" plus vibranium. In his attempts to discover what that "mystery something" was, MacLain invented Adamantium. That's why the shield is ofen referred to as an adamantium/vibranium mix, however, to be technical, it is a steel/"mystery something"/vibranium mix.
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Feel free to send in ideas for future debuts I should feature here to bcronin@comicbookresources.com!