This is "The Book of Knowledge," a feature where I spotlight instances where notable revelations that affect comic book continuity were first made in texts outside of comic book stories themselves. In other words, times when stuff like the Official Handbook of the Marvel Universe either introduced or resolved changes to continuity.

Today, based on a request from my pal Avash, we look at when Marvel first revealed that Captain America's shield was made out of vibranium.

Captain America's famous shield made its debut in the second issue of Captain America's self-titled ongoing series...

However, the shield originally was not indestructible, so Marvel never had to bother to explain what was so special about the shield. Heck, here it is literally being disintegrated in Avengers #35...

But quickly, in Tales of Suspense #93, it was reconnected that it WAS indestructible (and therefore, Cap must have had some other shield in that Avengers issue for some reason)...

Even into the 1980s, when Roger Stern, John Byrne and Joe Rubinstein went over Captain America's origins in Captain America #255, they don't explain WHY the shield is so special, just that it was a metallurgical accident...

Well, soon after Captain America #255, the Official Handbook to the Marvel Universe revealed that Cap's shield was made out of vibranium and adamantium...

There was a later issue devoted just to weapons and one again, they reiterated the combination...

And one last time in an article at the end of the issue (#15) explaining the history of adamantium...

However, since adamantium wasn't invented until Avengers #66, obviously Cap's shield couldn't be made out of a vibranium and adamantium mixture, so instead, Captain America #303 (by Mike Carlin, Paul Neary and Dennis Janke) revealed that the guy who created adamantium invented it in his attempt to replicate the experiment that made Cap's shield, which was vibranium and steel merged in some unknown fashion...

So when they say Cap's shield was "Adamantium," they just mean that Cap's shield was the ideal by which adamantium was invented based upon.

Thanks to Avash for the suggestion! I've done sooo many articles about Cap's shield, but somehow never this one.

Okay, folks, this sort of thing is something that happens all the time, so if you have any suggestions for future "The Book of Knowledge" features, drop me a line at brianc@cbr.com!