Nitrocellulose reactions with tuning machines

No mandolin content here, but very applicable to this forum and the collective knowledge of some of the folks here.

I pulled these circa 1940 Epiphone tuning machines off a (rather large) instrument today. There is a very distinct red color reaction around the tuning machines and string posts only where the layer of nitrocellulose finish has been removed slightly to allow for a good fit, exposing some unfinished maple. This is NOT surface level, but appears to be in or under the finish. The original finish was blonde, so it is not leftover color from fading. Could it be a deeper reaction with the sanding sealer? It is similar on both machines. I believe I am the first person to work on this instrument and remove the machines, "gold" plated 30s /40s era Klusons, hand engraved from the factory. I've never seen it before and am curious if anyone here knows.

The neck was broken in a couple of places, so it is getting prepped for a new European maple neck and a scroll graft. For the curious, the high quality seasoned European maple bass neck blank with decent figure and excellent grain costs approx. $450 just for the blank!

It would be great if we could keep the discussion on point with people who actually have nitro & finishing experience.....;););)

Looks like the reddish color is only where the open areas are........oil/lubricant reaction? No experience with this, just an observation, FWIW.

I wondered about that; possibly, but here is no sign of lubrication-very dry nitro. Whatever it is, the quality is strong enough that you could do a nice 'burst

I don't know...
but it looks like something from the metal of the tuner has infiltrated the wood under the finish. I base that on the color looking to be in the wood under the finish, and it looks like it followed the grain from the places where wood was removed to relieve the tuner gears and 'clamps' and those parts were in contact with unfinished wood. I don't think it has much to do with the lacquer, but instead is in the wood under the lacquer.

Notes:
It is not evident at the screw holes.
It is not evident at the post holes.
Those are also places where unfinished end grain contacts metal; why is there a difference?

What material are the gears? The screws? The posts?

What do the contact surfaces of the tuners look like?

Quote:

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Originally Posted by Jonathan Ward

What do the contact surfaces of the tuners look like?

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Look at the bottom of the image.

Could there have been something on the gear/assembly that was a lube from the factory. Would have been long since dry but may have stained decades ago.

Only a guess. But it looks very similar to residue from jewelers rouge. I've encountered a couple of folks that used jewelers rouge to clean and polish corroding metal parts on their instruments including tuning machines.

Quote:

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Originally Posted by MikeEdgerton

Look at the bottom of the image.

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Thanks! Couldn't enlarge the image on the device I was using.

Is it similar on the other side, near the D & G string pegs?
If so, I'm betting oil (heaven only knows what kind, back in the day) seeped through after a generous lube of the worms.

Quote:

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Originally Posted by Philphool

Is it similar on the other side, near the D & G string pegs?
If so, I'm betting oil (heaven only knows what kind, back in the day) seeped through after a generous lube of the worms.

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Haha, first thing I thought... Marvel Mystery Oil!

Does the other side look similar? It looks like the red coloration is not down in the relieved areas.

The color and placement cause me to wonder about faded stain in the finish. This reminds me of a book I read from the Taunton Press (Fine Woodworking) by George Frank, "Adventures in Wood Finishing". He described an event where his company had finished a batch of oak desks for a bank, and the bank didn't like the red orange color. So he and his crew sealed off the huge room and fumigated with ammonia for a few hours. I don't think he said anything about what else was affected by the fumigation but the bank was very happy with their new golden amber desks.

Another thought is some strong color used similar to chalk fitting to bed the lumps and bumps on the "inside" of the tuner plates. The fact that the color appears at the points where lubrication would be applied is another point of interest.