Quote:
Originally Posted by Todd Yates
This is a common reaction between lacquer and pressure sensitive adhesives. You see the same thing after removing a pick guard. It's not always obvious unless you get the light right, but I can nearly always spot it.
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Todd is completely correct about why this occurred: it didn’t happen because of any “chemical reaction,” it was the result of mechanical compression of a finish that was too soft for some reason.
The only time I’ve experienced anything similar was when I took delivery on a custom made guitar that had been sprayed with what turned out to be a defective batch of lacquer. The finish on that guitar never did fully harden.
A couple of years later I ended up trading the guitar back to the builder, and when I removed the armrest in order to be able to reuse it on another guitar, there was a similar imprint underneath it as L20A has described.
John Pearse himself always cautioned me to never put an armrest onto to a guitar with a nitrocellulose lacquer that was newer than six months old, because the finish needed to fully harden before an armrest should be mounted, for the very reasons I’ve just explained.
So if an armrest is put on a new guitar with a finish that hasn’t fully hardened, or there’s some problem with the finish (which is more common with factory-built guitars than you might expect,) then this sort of imprinting can occur. It doesn’t even have to be nitrocellulose, either - in fact, some the modern “catalyzed lacquer” finishes can be the worst culprits in this regard.
Quote:
Originally Posted by Todd Yates
The good news is that it will diminish some with time. I wouldn't do anything immediately. Give it at least a month, then consider wet sanding (with a block, not your hand) and buffing. No finish work is quite that simple, and don't undertake that yourself if you're not skilled in working with delicate finishes. However, it can be made near invisible.
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To which I’ll add is that the unfortunate thing about this, in addition to the damage and distress that L20A is dealing with, is that at least half to two thirds of the people who read this discussion will skim the posts, then walk away under the impression that it was this Pearse armrest’s adhesive that caused a chemical reaction.
Even though that isn’t what happened at all.
It won’t matter. Many folks will glance through this thread, the phrase “chemical reaction” will jump out at them, and that will be their takeaway.
For you hands-on types, however, I can show you a way that replicates exactly what happened with L20A’s guitar, and you can do this in your own home kitchen.
Get two slices of bread, a jar of peanut butter* (creamy, not crunchy, if you have some) and a carrot. Spread a layer of peanut butter on one piece of the bread, then slice the carrot into 1/4” strips. Place some of these carrot slices 1/4” apart onto the peanut butter layer, then place the second slice of bread over that, and press down.
Then eat hearty!
No, I’m kidding; you’re not done. Lift off the second piece of bread, then lift the carrot slices off the layer of peanut butter.
What you will see is a succession of lines in the exact shape of the carrots slices that were there only a moment before.
That’s what happened to the finish on L20A’s guitar: a form of mechanical compression, nothing more.
Hope that makes sense.
Wade Hampton Miller
*If you don’t have any peanut butter, cream cheese will work equally well. A cream cheese and carrot sandwich might even be better, too, once you take off your lab coat and settle down for a tasty snack!