Crater In Finish Along Book Match Line

[Ruffone]

Okay guys, I have a 2011 Custom 24 Dave Navarro Signature and I’ve got a question for the masses. The other day I noticed that there is an indent on the top of the guitar right on the top of the book match line. It follows the line from the neck all the way to the bottom edge of the maple cap. The finish isn’t cracking but seems like it is sinking into the book match seam. I reached out to PRS and asked them about the indent and I got the craziest response back. They said, “The finish used on our guitars is of a very thin specification to allow the best vibration transfer and sustain out of the instrument. Because the finish is so thin, it will gradually sink into the grain and glue lines of the wood. This is normal for the finish..”

I currently have six US made PRS guitars, all of them but one is older than this one and none of them has ever done this. I’ve never heard of this happening to a guitar’s book matched top. What’s your experience, has this ever happened to one of your PRS guitars or have you ever heard of this happening? They stated that this is normal for the finish???

 

[aphantomvaper]

Yes this is wood and these things happen. The finish can shrink and sink and the wood can change also to draw the finish in. Do not worry...IMHO.

 

[sergiodeblanc]

Totally normal

 

[JasonE]

It definitely happens. It is something that happens to all guitars at the same level. I have seen it with guitars of the big G and F brands as well. I have seen some older PRS CU24 guitars where you can can see how the finish has sunk into the wood and you can see the grain. Some people love that this happens. It gives the guitar some character as it ages.

 

[ElrytNamrogo]

Yep, totally normal.....all my PRS guitars have this in some level of degree.

 

[21Hemispheres12]

I noticed the same thing on my black top SSH. I think it’s just more noticeable on opaque guitars.

 

[garrett]

I'll add that it's quite common and in no way limited to PRS. It can happen anywhere two pieces of wood are joined together and it may sink into the grain a little bit as well.

 

[RickP]

As @garrett notes, it can show in any part of the wood where there are joints or pores… which is almost anywhere. I’ve got guitars from the 70s that don’t show it and newer ones that do. In my experience, acoustics show it more, possibly from the softer spruce top. I don’t know why one shows it and one doesn’t, other than the inherent inconsistencies of wood and workmanship.

 

[Alnus Rubra]

I’ve a non PRS custom made acoustic and the lacquer has sunk into the wood grain. Totally normal.

 

[caribbeansun]

Good information, I would never have thought this would happen either.

My background is not using finishes like these - we use a coat of sealer to prevent this which closes the grain but we aren't painting guitars obviously.

 

[Ruffone]

Well my collection is well over 30 guitars of mixed brands and mixed finishes and non of the electrics have ever done this before. Yes, my acoustics have but not a single one of my electrics have.

 

[caribbeansun]

I gave this additional thought and it suggested a couple of things:

First, the nitro must not cure, it has to retain some liquid qualities since a solid can't be absorbed.

Second, if it does cure is there some element that can trigger the solid to return to a partial liquid state? I see this daily with solvent based paints and topcoat and toluene. Toluene creates heat, returning the pain t to liquid form which can then be wiped off to clean the piece.

Some googling turned up a few sources stating nitrocellouse doesn't cure because no catalyst is added. Thus hypothesis one seems to hold true.

I also found a site claiming that nitrocellouse is 30% solids compared to 70% for some poly finishes. I find both of these figures highly questionable, however, lower solids would indeed reduce resistance to change over time. I could not find anything definitive on the percentile.

I also found references that suggested heat and humidity could cause issues. I would guess the heat could well reactivate the liquidity of the nitro and of course we know humidity opens up wood, a combination of these would seem quite problematic.

Lastly, heat and humidity at time of application will cause wild swings in the time required to dry each layer same as any other finish. Guitars finished in the winter would likely result in better finishes as the grain contracts and the finish dries properly.

One of the better written resources I found was this thread on a Luthier site: https://www.luthiertalk.com/threads/the-plain-truth-about-nitrocellulose-finishes.239/

Hope some of you find this helpful as it answered some unanswered questions I had.