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The backstory: I’m nearing the end of applying a French polish finish to a pair of guitars. I have been spiriting off with alcohol, and everything is going well. I decided to also give the guitars a once over with naphtha to capture surface oil. The naphtha really left everything looking not quite right. I’ve used naphtha in the past without a problem, but now that I think about it, I was using the Behlens naphtha before when it was fine. This time, I used a newer can from Lowes. I recovered from the weird look by applying another session with the shellac and spiriting off with just alcohol, so no worries. But I’m done with this can of naphtha, and maybe all naphtha for a while. I’m curious if anyone else has had problems like this.

Yes.

Got a picture?

No photos; I wanted to fix it ASAP, so that moment is gone. It was way splotchier than I remember from when I used the Behlens naphtha on prior guitars (splotchy is to be expected, but this was way worse), and there were a few tiny spots where it looked like it left some sort of white deposit when it dried. I know, we would all suspect that the white spots are pumice that had been transparent before due to oil, but the naphtha took away the oil. I really doubt that, because those spots were clear before I introduced oil into the process. Also, my spiriting off with just alcohol has not caused the white spots. Is it possible that some additive in the naphtha (again, hardware store naphtha, not Behlens naphtha) is not as kind to shellac as a purer version of naphtha? Anyway, that’s a mystery I will not be sleuthing out. I just want to move forward and get these guitars done. No more naphtha for me unless I buy some more Behlens. But I wondered if others had seen this happen.

Don, did it happen to look like this?



I had this happen on a FP uke and I never figured out how it happened. I too use just naphtha from the hardware store.

Brad


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Brad—

Yes, it was a lot like that, but more of it. I think that’s not unusual with naphtha and French polish; if the oil gets stripped away without also smoothing out the shellac (a benefit of using alcohol), it will look splotchy like that. But I had more of that, plus the white spots, so it felt like it was worse than it should be. Yours looks fine in comparison.

Ok, good to know. It did clean up with more shellac, but I hadn’t seen it before.

Now, if I can just figure out how to keep the HHG from distorting the finish on the bridge perimeter, all my FP mysteries will be solved.


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I/ve used naptha to speed up,oil based varnishes, in colder weather turpentine to slow it down in warmer weather . My guess is the addiitves in the naptha reacted with the shellac and fp in a negative way ??

Not all Naphtha are "pure". Klean strip for example lists it at 95 to 100% light hydrotreated naphtha on the SDS, which means it can contain up to 5% other substances that don't need to be listed (probably water, which might leave a white haze). V,M,&P Naphtha is usually pretty pure (paint thinner less so) but fresh, not fully cured finishes will sometimes react with it.

Interesting. I was just cleaning up an FP guitar with Lowes naphtha and have no issues at all with it. In fact I thought it was common practice to use naphtha with FP.

The stuff I am using is Sunnyside brand naphtha

Another reason I do not use oil in my FP.....

The problem is likely the fats in the oil and not the solvent. Solvents are made very consistently and labeled incredibly well as they are dangerous, Olive oil not so much....

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Don, what kind of oil are you using? I use walnut oil mixed in with the shellac. Brian makes a good point, could be reacting with what ever oil you are using.

I've been using olive oil (Spectrum brand, fresh bottle) for lubrication, but in the last few coats I added in some walnut oil (again, Spectrum brand, fresh bottle) in the shellac bottle itself. In retrospect, that is probably the issue. While the olive oil is supposed to completely migrate to the surface, and much of the walnut oil does, too, some of the walnut oil is supposed to stay in the finish. That part of the walnut oil probably reacted badly to the naphtha. Lesson learned. No more naphtha while I am incorporating oil into the finishing process, especially oil that is meant to leave a little bit of itself behind. No real harm done. The later coats went on fine and alcohol spirited off the excess oil without issue, and the white spots are gone. The finishes are looking good enough to let them sit and harden for a while. Thanks for the help, everyone!

Don, I don't know about the Spectrum brand but is the walnut oil 100% pure? That's very important when mixing walnut oil with shellac. Like I said I use walnut and have no problem with naphtha.

I feel confident that the Spectrum brand is 100% pure walnut oil based on the following:

1. It is labeled that way.
2. I have read in the articles on French polishing that Spectrum is good for this job, because it is 100%.
3. The Tom Bills videos show him using Spectrum walnut oil.

Well hummmmm.... I'm at a loss then.