Tricky Crack Diagnosis Issue

[Dave Domizi]

Hi,

My name is Dave Domizi and I run The Fret Shop in Athens, GA. I hope that you’re all well.

I’m writing to ask for any experienced ideas that you might have for sorting out a trickier crack diagnosis issue (finish crack vs wood crack) that came to me today. The guitar is a 1967 Gibson Hummingbird that has had various owners and is changing hands again from a previous customer of mine to a reseller as part of a trade.

ISSUE: The back of the neck has a roughly 6” long, tight crack that starts about 1/4” inside of the high-E tuner plate and runs somewhat diagonally across to the bass side/down the neck toward the body across the V-carve transition area behind the nut, ending roughly 3/4” from the binding/edge of the neck, roughly 3” past the nut. This is a strange one - not a traditional headstock break, maybe not a break at all. Rather it may simply be a finish crack, or it could be a stress crack in the wood, possibly from the internal truss rod hardware. The guitar hasn’t been abused or suffered any obvious hits/dings on the neck, and it has been stored in proper climate. 

Under mild magnification, the crack does not show any visible signs (larger dark shadow line) that it is open/deep, and light pressure grabbing and gently flexing the headstock did not appear to change this, ie - it doesn’t appear to move under light force. I wouldn’t want to apply heavier force out of concern that it could cause further damage, even if only aesthetic. I suppose it’s possible that 53 years of internal force from the truss rod/anchor could cause such a crack in the wood, but there is no significant doming/bubbling/spreading open of the crack to indicate this definitively.

QUESTION: Are there any additional techniques or equipment that should be considered (x-ray, MRI, dry ultrasound, high powered magnification, etc) that might help to determine the actual nature and depth of such a crack? The involved parties need a definitive diagnosis to aid in the deal & reselling process, and I am unfamiliar with how porous wood grain/wood filler/finish/etc would behave under these techniques, and whether it’s even possible to achieve this goal.

I’m very grateful for your time and any thoughts and info that you might have. Stay healthy & well.

Thank You,

Dave

[Greg Mirken]

It's certainly an unusual place for a lacquer check. Does the instrument have other examples of checked finish?

From your description I gather this runs sort of diagonally through the neck. Does the grain at the top of the headstock exhibit the same orientation? That would be an indication of a wood crack.

[Len Biglin]

To me it doesn't seem to follow the grain , so i doubt its a crack in the wood . Could it be a scratch ? my thoughts are to get some clean water , maybe add a dash of alcohol to reduce surface tension , run a few drops along the crack while gently twisting the headstock , if its a crack in the wood some water should wick / run in there , and will bead in and out as the headstock is twisted . That should establish if it is a crack , then you can decide if epoxy or HHG will best penetrate , I would probably use epoxy thinned with alcohol , perhaps a plastic straw over truss rod .

[jbbancroft]

Instead of water use Naphtha, it will easily wick in if it is a crack, water can swell the crack. Apply Naphtha to the crack in small section, then flex the crack slightly. If it is a crack you will actually see the Naphtha moving and going into the crack. If your vision is a little on the poor side use a headband magnifier to view the crack and Naphtha.

My gut feeling is it is just a Lacquer check, but if it is a crack I would use thin super glue, as it will wick it’s way completely into the crack.

Jim

[Greg Mirken]

Well, as long as you're trying to wick liquids into the crack, why not just try to wick thin superglue into it? If it does wick in, not only do you identify it as a crack, but you glue it at the same time. With a little clean up and buffing the repair should be close to invisible.

[jbbancroft]

First you want to find out if the wood is cracked, Naphtha will determine that. Then if you actually have a crack in the wood use superglue to repair it.

Jim

[Len Biglin]

Dave seems to be experienced but I'll just mention that a bit of tape each side of the crack will minimise superglue/lacquer mess , not a problem with epoxy as it cleans up nicely with alcohol or turps.

[Greg Mirken]

What was the verdict, Dave?

[Dave Domizi]

In the end, the consensus was that it was checking, and the guitar has been sold. I wasn’t convinced that any repair was needed and, given that the guitar was about to be sold again, the expense and the risk of even the smallest visual evidence of a repair inclined all parties to leave it alone.

The guitar had previously sold in 2018 through Chicago Music Exchange, and they felt that it was just checking. There was only one pertinent photo from that sale that did show the upper part of the crack on the headstock, and it was consistent - the crack stopped at the same place by the tuner. It would have been great to have a lower shot that showed how far down the neck the crack extended/whether it had changed, but regardless it seemed very tight and stable.

I posted here mostly because I was curious to know if anyone had previous experience with other high tech crack scanning options, just for these unusual situations, especially in dealing with expensive vintage instruments.

Thanks to each of you for your input!