Whadda you think happened here?

[Caberguy]

My relatively new-to-me 1991 Flatiron came to me pretty surprisingly clean (save for a bit of tarnish), with the exception of this little bit near the bridge. It was clearly under the bridge at some point, but the intonation is pretty close where it is right now.

Any thoughts on what caused this? Just years under string tension? Years under string tension with a bridge that was leaning forward compressing the wood fibers there? Bridge put on before finish was cured? Left in a hot car and the finish got soft?

It's a bit rough to the touch, but not really that big of an indentation. And, as you can see from the wider shot, it's not really that noticeable.

I'm really not worried about it, just curious.

[sunburst]

Looks like the bridge was sitting in the wrong place for proper intonation, and was there long enough to imprint the finish. Nearly any finish will imprint like that given time. The fluting of the top finish might indicate that the mandolin has gotten hot, but I'm only looking at a couple of internet photos so I can't really say.

[Chris Pile]

Some doofus tried to move the bridge while the strings were at full tension.

[20MartinA]

The finish may not have cured completely when the bridge was in the wrong position.

[Tavy]

+1 on what John said: you see that under the bridge of most instruments if they're old enough. Normally you don't get to look under there, but in this case the bridge was clearly in the wrong place for some time!

[Simon DS]

Maybe it had a different tailpiece before, would that explain the bridge being in a different position?

[sunburst]

Nope. String length from nut to bridge determines intonation (along with action height, string gauge and string tension). The tailpiece has nothing to do with that.