That "I" turning into an "L" is not corrosion, nor did being stored somewhere for a long time cause it. I will agree with some kind of damage, either environmental or from a damaged die. It is pretty cool to look at though.
Never a good idea to wash a coin at all. When it was dirty it was worth 5 cents, after washing it's worth 5 cents! better luck next time!
My take is a very extreme hit to the B separating it. Being close to the I it looks like it might be something else, but I'm going with damage. JMHO.
Exactly as Tommy said the B took a hit which makes it look separated. As far as the IB it has joined from circulation wear and tear.
I can see how the lower part of the "B" took a hit, But I can't see how that hit would move the material perfectly in way to form a bridge to the lower "I". I can also see LDS on this coin so maybe it's part of a worn die issue.
It looks like a elongated die chip/break underscoring the B extending from the I. Dies will have typical areas of weakness...pinch points...that are more likely to fail at some point. You see this on LIBERTY on Lincoln Cents and usually along the tops of the devices adjacent to the rim on the Obverse of Jefferson nickels. I've not seen a chip/break like that in that particular spot, but not out of the question. No premium this time...but keep that in mind when you got to 'clean' a coin. Conserve the coin to be conservative if you think it has any potential value. One member here posted a 1909 S (VDB) heavily corroded. They asked questions before doing anything...especially on a coin like that where values could be over $100 or much more if they find the VDB. This was a good nickel to experiment on as it is a spender...unless you like that for a reference piece in your collection.
I just wanted to find something cool. Lol. I am new to this and extremely anxious to make my first discovery. As for the coin, I suppose the only enjoyment I will be getting from it has been to see everyone's interest in the anomaly it generated for discussion. If you would care to have it for a more complete study on what may have actually caused it to happen, just reply and let me know where to send it. Thanks.
I think that with each step, you are getting to a better point in developing your eye for varieties/errors. It takes some practice, and this specimen was just that. It did not appear normal to you, and while indeed it does look peculiar, it's a natural phenomenon that occurs as the die ages. What is really interesting is when an early die state strike shows evidence of premature failure. Of course, there are the usual suspect places to find damage to the die (due to wear and tear). You've probably noted the cracks that develop from the corners of the Monticello or the Lincoln Memorial. Stressors in the design attract the focused energy of the strike/press. The die gives up. Or damage when a pair of dies contact each other without a planchet. Looking at each design for each denomination, you'll quickly identify where the typical wear-and-tear events occur. Normally, not much if anything for a premium. But certain wear-and-tear events do get some extra attention: BIE cents, 3 or 3 1/2 legged buffalo, 2 or 2 1/2 feather indians, 1922 Plain LWC. Wear-and-tear, grease filled dies, aggressive die maintenance....etc., etc., etc.,...lots of ways to change the look of a coin from subtle to significant. It makes the hobby interesting for a number of us. But to many others, a lot to do about nothing (e.g., it's just the natural progression of a dies life). To each their own. Collect what you like...like what you've kept...even for a little while.
I just replied to you in the other thread and then came here to read this one. This one just verifies that you understand my frustration because you can remember what it was like for you when you first started trying to figure it all out. There is a lot to take in. I actually have another coin that caught my eye but I was kind of leery of posting it. LOL. But I would really like to understand what happened to cause what I saw. Is there a means through which I can present it to you without embarrassing myself again? I don't see a way to use this window to send it to you.