Early poly melt

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Gavanti
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Early poly melt

Post by Gavanti » Thu Apr 12, 2018 6:22 am

I'm curious why late 60s-early 70s poly seems to interact so badly with other materials. I realized the other day that my strap has been eating the finish on my '68 Jag around the strap pins (grrr.), and some of the most intensive finish damage I've seen has been on Mustangs and Jazzmasters from that era. I've had no problem with the same strap on nitro or on more recent poly.

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Kinx
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Re: Early poly melt

Post by Kinx » Thu Apr 12, 2018 6:49 am

I have similar issues with finish on my '72 JM. It is most apparent on the back, since the guitar sat in it's case for a long time - the upper part of the body has finish checking from touching the bottom of the case, I will post photos after I get home.
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jeff m.
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Re: Early poly melt

Post by jeff m. » Thu Apr 12, 2018 2:21 pm

This is interesting ! I have a Blonde '76 Strat that has intense red discoloration around the upper & lower strap buttons, with a few random patches on the top..I'd always assumed that a previous owner had always cased-up the guitar after sweaty gigs & the discoloration came from the finish reacting with the case lining.

Looking at it again - after reading these posts- I'm now inclined to think the red stains are from a strap that was left on the guitar in the above scenario i.e; sweaty guitar + sweaty strap, straight into case post-gig.

I think you're right, Gavanti..late '60s/ '70's poly finishes were susceptible to contact with other materials..when you think about it, poly was a new 'technology' for guitar finishes at the time, after years of nitro..bugs were probably being ironed out at the time..( this particular Strat is an interesting shade of 'nicotine yellow', too ! Patches of the original white poke through here & there in the usual contact spots ).

Thanks for the interesting posts, guys..interesting to get a different take on a guitar I've had a long while !

Best,
Jeff.

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Re: Early poly melt

Post by mackerelmint » Thu Apr 12, 2018 3:39 pm

This IS interesting. I've always preferred poly finishes because nitro reacts to stuff. But this makes me wonder if this discoloration is a product of age, and the finish is breaking down? Or maybe the formulas have changed over time? If my poly finished guitars get nasty years down the road, I'm gonna be groaning about the pointlessness of my aversion to nitro. ;D
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Re: Early poly melt

Post by Kinx » Tue Apr 24, 2018 10:03 am

I've tried to capture aging of the finish of my 1972 Jazzmaster. If I wouldn't know better, I would say it's a nitro.

https://www.dropbox.com/sh/row0c157fv6n ... 4nUFa?dl=0

check out the finish checking on the upper horn in the picture below.

https://www.dropbox.com/s/8tqbeyjnxgb61 ... 1.JPG?dl=0

I suspect this is a result of a long time of sitting in it's original case.
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Embenny
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Re: Early poly melt

Post by Embenny » Tue Apr 24, 2018 3:10 pm

My understanding is that the early poly finishes interact with the plasticizers in vinyl straps. These are molecules that are meant to keep the plastic pliable so that the strap doesn't crack as it's bent back and forth over time. Once they dissolve into the poly, they do the same thing - make it soft and pliable instead of rigid and crack-able. Hence the irreversible gooey-ness.

Modern poly finishes are generally catalyzed to my knowledge, whereby their molecules are more "fixed" in position, if you want to imagine it that way. That prevents things like those plasticizers from getting in-between the chains of molecules and compromising the structure.
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Re: Early poly melt

Post by Jaguar018 » Thu May 03, 2018 5:53 am

mackerelmint wrote:
Thu Apr 12, 2018 3:39 pm
This IS interesting. I've always preferred poly finishes because nitro reacts to stuff. But this makes me wonder if this discoloration is a product of age, and the finish is breaking down? Or maybe the formulas have changed over time? If my poly finished guitars get nasty years down the road, I'm gonna be groaning about the pointlessness of my aversion to nitro. ;D
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