What’s going on with my finish? (NMC)

[multidon]

I have a Martin D-17, not the old all mahogany one but the more recent one, early 2010’s, with a shaded spruce top. The mahogany body is matte finish but the shaded spruce top is glossy. I don’t remember where I read it or heard it, but my understanding is that the matte parts are some kind of poly, but the shaded spruce top is nitro. I’ve owned the guitar for several years now. I like playing it but it’s a case queen, only getting played occasionally and never gigged. I just noticed some lighter spots developing on the top that look like they’re under the finish. I wouldn’t call them white but definitely lighter. Most of it is in the upper bouts. In the worst spot they form two concentric rings. I do humidify them guitar as I do all my instruments in winter. I theorized that maybe it was over humidified and left it out to dry for a couple of days to see if the marks went away. They did not. I tried to photograph what’s happening but it can’t be photographed. I will say on this particular model of guitar, they produced the shading of the top with some sort of new process, the details of which I don’t know. They only made these shaded tops for a couple of years then stopped, changing the 17 line completely to all matte finishes. Makes me wonder if they had problems with fading dye on these. But the top being gloss nitro also makes me suspect moisture. Anyone have any ideas as to what I have here? Anything that can be done? You can only see the defect if the light hits it a certain way. Thank you in advance for your advice!

[Buck]

They used a C.A.B. (cellulose acetate butyrate) on gloss top guitars and full satin necks at the time, still do actually. They don't use "poly" finish on any guitars, other than the older Sigmas that were imported and some of the imported electrics. I've seen a fair number of those D-17's and don't recall seeing anything like the problem you described. Obviously you're seeing it, but whatever it is, I don't think it's a widespread problem with that finish. I'd likely have heard about it if it was. Without seeing the guitars or photos I really have no idea what it might be.

Do the spots correspond to anything in the case, or the case itself, that might be touching the guitar in those areas?

[Richard500]

CAB is biodegradeable and mold can grow in nice circles, but unknowns are many. Additives to the coating, something breathed onto the bare wood, some topcoat of wax +++. You’re not likely to identify the problem, or the cure. You may want to have a good look inside with a mirror and a strong light.

[Jim Garber]

Many years ago when I owned my 24 F4 I took it out for a gig (remember those?). When I opened the case there was a small puddle of condensation on top of the mandolin. I wiped it off but saw a whitish area in the finish. I think this was similar to someone not using a coaster for placing a drink on a fine piece of furniture. I took it to my then current wizard of a luthier and he judiciously used a heat lamp to make that under-the-finish moisture disappear. I would not try this myself but he definitely knew what he was doing.

I don't know if that is the problem you are having but you did mention the possibility of over-humidifying the guitar.

[multidon]

I probably wasn’t clear about the two concentric “rings”. They are not round but more oblong and pretty irregular. Fairly certain this is not mold. It also occurs on other parts as blotches.

Thank you Buck for setting me straight on exactly what the glossy finish is. Do you know what they used for the matte finish at that time? Just curious, those parts of the guitar are fine.

Yes Jim, ultimately I may have to take it to my luthier. I had thought about maybe judiciously using a hair dryer on it but fear of what could go wrong stops me.

[Bob Clark]

Hey Don, sorry to hear about this problem and I sure hope you can resolve it. Have you thought about contacting Martin directly to ask whether it is a problem they are aware of and if so, how to fix it? They seem to be very approachable, and very customer oriented.

[Buck]

Thank you Buck for setting me straight on exactly what the glossy finish is. Do you know what they used for the matte finish at that time? Just curious, those parts of the guitar are fine.

Same finish but in satin, which is the same finish they use on the necks of most Standard Series guitars.

[multidon]

It always amazes me how asking a question on this forum yields information that sends me in a completely different direction! Cellulose Acetate Butyrate? Never heard of it! So I did some research! It’s fascinating stuff! It has a lot of characteristics that I can see would make it attractive for instrument makers. It contains cellulose, just like nitro, but is completely water clear, and stays that way. It’s low viscosity with a high solids content, making it easy to spray. It resists cratering and orange peel, and levels itself quite well. When dry it’s water and UV resistant. It really sounds like an ideal instrument finish. I wonder, what other instrument makers use it? Is it something a small shop or single luthier can get, or does it only come in industrial quantities? I know we are getting off topic, but my curiosity has been piqued. After three days of drying out there is little effect so far. Since this stuff is supposed to be water resistant, I wonder if there is some kind of de-lamination taking place. Then again, if it’s a cellulose compound, does that mean it “breathes” like nitro? If so then water vapor could get in.

[multidon]

On a whim I tried some very mildly abrasive guitar polish on the spots and with some elbow grease they disappeared. I thought I was dealing with something under the finish but guess it was really on the surface.

[Bob Clark]

On a whim I tried some very mildly abrasive guitar polish on the spots and with some elbow grease they disappeared. I thought I was dealing with something under the finish but guess it was really on the surface.

Congratulations! That sure is good news.