This may be out in left field, but...

[Pdubs76]

Would a gloss finish on the inside of a guitar as well as the outside make it anymore resistant to humidity changes? Or does the wood need to breath?

[airborne1]

I would guess that it would impede the vibrations, losing tone.

[gr81dorn]

Originally Posted by Pdubs76

Would a gloss finish on the inside of a guitar as well as the outside make it anymore resistant to humidity changes? Or does the wood need to breath?

From a finishing standpoint, sealing wood from all sides would help it be more stable. Certain finishes better than others. Water may still try and escape and cause bubbles which can cause cracks in the finish...other similar things can happen so the wood really would still need to be handled with similar care to keep it pristine, but it would be more stable.

Tone-wise - who knows? I can see arguments both ways.

[srick]

Simply, it would slow down the exchange rate of the moisture.

There are examples out there of acoustics that are shellacked on the inside, but it’s rare. As far as its effect on the sound and tonality of the instrument, I think most experienced luthiers would agree that there are other components of the build have a far greater contribution to an instrument’s sound.

And they would all likely agree that that the thickness of the finish has a greater effect on the tone.

Best,

Rick

[Wade Hampton]

There are a number of handbuilders who seal the interiors of their guitars with thin layers of finish - it’s not at all uncommon. Applied judiciously, it doesn’t hurt the sound, but DOES help stabilize humidity levels of the instrument.


Wade Hampton Miller

[Robin, Wales]

It may possibly change the tone. As a guess, I would expect the wood to have a little less damping and perhaps act more like a harder wood (mahogany sounding more like maple or maple sounding more like rosewood). But that is totally a guess on my part.

[Guitarplayer_PR]

Originally Posted by Pdubs76

Would a gloss finish on the inside of a guitar as well as the outside make it anymore resistant to humidity changes? Or does the wood need to breath?

Gloss finish in the inside? WHY?

[Pdubs76]

Originally Posted by Guitarplayer_PR

Gloss finish in the inside? WHY?

Just wondering if the gloss would create a barrier against changes in humidity.

[Hey_day]

Originally Posted by Wade Hampton

There are a number of handbuilders who seal the interiors of their guitars with thin layers of finish - it’s not at all uncommon. Applied judiciously, it doesn’t hurt the sound, but DOES help stabilize humidity levels of the instrument.


Wade Hampton Miller

Do you know what builders do this?

[KenL]

Alvarez Yairi used to finish the inside back and sides of some of their higher-end guitars.

[rstaight]

Being a wood worker I at least stain all sides of a project to help stability. Doesn't matter if you can normally see it or not.

Sometimes I will do staining before final assembly.

I guess one way to get an idea on tone is to build 2 instruments out of materials from the same tree. Build one with a thin coat of finish on the inside and one with out. Then you may be able to determine if there is a difference.

If there is no discernible difference I would finish inside and out for stability.

[stormin1155]

The late Dave Plummer finished the inside of his guitars. I'm sure it would have some impact on tone. Whether good or bad would be up to the ear of the behearder.

[hermithollow]

Glue doesn't stick very well to finish. Finishing the inside of an instrument makes repair a bit more difficult.
Thin finishes offer some protection from dust and dirt, but not much else, and are used to not impact the sound of the acoustic guitar.
Most makers believe the disadvantages of finishing the inside of an acoustic guitar out weigh the advantages.

[TomB'sox]

Originally Posted by Hey_day

Do you know what builders do this?

I know two very famous and fantastic luthiers that put a single coat on the inside of the back, Jason Kostal and Ben Wilborn. There are likely many more as well. It makes them less susceptible to humidity changes and therefore cracking. I know both these guys personally and can tell you, if it had any effect on tone, they would not do it, period. These guys are all about tone.

[airborne1]

On closer inspection, my Eastman 40 OM appears to have a thin finish on the inside.

It sounds great to my ears.