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Thread: How to identify lacquer vs. varnish finish?

  1. #1
    vintagemandolin.com Charles Johnson's Avatar
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    Default How to identify lacquer vs. varnish finish?

    Is there a quick positive chemical test to tell lacquer from varnish? I know about testing in an non-visible area (under the tuner plates or tailpiece).

    How long should I let the solvent contact to finish to be certain?

    Thanks
    Charles

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    Default Re: How to identify lacquer vs. varnish finish?

    Here is a previous thread on the same subject:

    http://www.mandolincafe.com/forum/sh...h+test+solvent

    They never really did reach any agreement about the solvents.
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    Default Re: How to identify lacquer vs. varnish finish?

    Lacquer thinner is a mixed solvent consisting mainly of mid-molecular weight alcohols, ketones, and aromatics. It is generally more polar than the solvents of oil varnishes. The latter are largely aliphatic hydrocarbons. For NC lacquer, the ketones (e.g., acetone, MEK) are more agressive solvents than the alcohols. If you wipe some denatured alcohol on a lacquer finish, the finish will be dulled, but not so quickly and thoroughly dissolved as with ketones or the complete lacquer thinner mixture. The dulled lacquer film can be buffed back to gloss. Try a bit of denatured alcohol on a cured oil varnish finish, and nothing should happen. So I would use denatured alcohol to distinguish between the two. How long? Not long at all - maybe 10-30 seconds.

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    wood butcher Spruce's Avatar
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    Default Re: How to identify lacquer vs. varnish finish?

    Thanks for that!!

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    Registered User sunburst's Avatar
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    Default Re: How to identify lacquer vs. varnish finish?

    A word of caution:
    Some varnishes are spirit varnishes, are shellac based, and can be dissolved with alcohol. The big problem is; so many things can correctly be called varnish that "varnish" doesn't mean much. Acetone or lacquer thinner might be better to distinguish between a spirit varnish and NC lacquer, and we're right back under the tuner plate again.

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    vintagemandolin.com Charles Johnson's Avatar
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    Default Re: How to identify lacquer vs. varnish finish?

    Thanks all. The previous lack of a definite answer lead me to post the question again.
    Charles

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    Default Re: How to identify lacquer vs. varnish finish?

    John, what fraction of modern "varnish" finishes do you think are not oil or 'alkyd' varnish (e.g., Behlen's Rockhard or Pratt & Lambert #38, or etc.)? Certainly the pre-lacquer vintage mandolins had "spirit varnish" or shellac-based finishes, and the 'Behlen's Violin Varnish' is a spirit varnish. Also, some modern 'varnish' finishes are shellac-based French polish over an oil varnish. But for my 'varnish' finish or yours, I'd still say that alcohol would be the way to tell them from lacquer. Certainly, when in doubt, test under the tuner plates. Come to think of it, I use a mixed alcohol/acetone solvent for shellac for pore filling. I'll have to try it to be sure, but I suspect that acetone will also attack shellac or 'spirit varnish'.

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    Registered User sunburst's Avatar
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    Default Re: How to identify lacquer vs. varnish finish?

    I don't know percentages, but I do know that some mandolin builders have used (and do use?) prepared violin spirit varnishes, and I know of one builder who has used pure shellac and referred to it as "varnish", not incorrectly.

    BTW, the shellac, alcohol and acetone filler ended up working pretty well on the guitar. The back still looks like glass a few weeks after buffing the finish.

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    Adrian Minarovic
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    Default Re: How to identify lacquer vs. varnish finish?

    I'd add that alcohol may attack (or soften) oil varnish as well, especially when there is FP over thin oil varnish layer. I'm finishing work on one of my older mandolins and while touching up some chipped areas with shellac varnish the whole layer of surroundiong finish softens considerably.
    I'd prefer lower grades of alcohol for testing, 80% should be strong enough to soften spirit varnish but not soften oil varnish.
    BTW, the varnish on old Gibsons was most likely not spirit varnish but oil varnish. The traces of application can be found which are typical of oil, not spirit and there was a thread several years ago where someone cleaned lacquer overspray from his F-4 with acetone and it didn't eat the original varnish.
    Adrian

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    Default Re: How to identify lacquer vs. varnish finish?

    Adrian, you have your chemistry a bit mixed up. The FP over your oil varnish layer is literally a spirit varnish, and alcohol will attack it. However, it will not attack the oil varnish underneath. Oil varnishes form a polymer film by reacting with oxygen in air. Once the film has 'cured', the original solvent will not redissolve the film. About the only things that will attack an oil varnish are alkyl halides, such as f'rexample methylene chloride or 1,2-dichloroethane. The FP spirit varnish, unlike oil varnishes, is sometimes referred to as a 'solvent' finish, since it forms a film by solvent evaporation, and can always be redissolved by the original solvent. In that respect, FP and spirit varnishes have more in common with NC lacquer.

    It was my understanding that the Loar-era Gibson mandolin family instruments were oil varnished with an FP topcoat, but the pre-Loar era mandolin family instruments had spirit varnish or FP finishes. In my experience, every pre-Loar era mandolin or mandola I have dealt with had a spirit varnish finish, not oil varnish. I am sure that someone will come along and document some exceptions to that, but it is certainly my experience.

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    Registered User sunburst's Avatar
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    Default Re: How to identify lacquer vs. varnish finish?

    Same here, some kind of spirit varnish on pre-loar Gibsons in my shop.

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    Default Re: How to identify lacquer vs. varnish finish?

    Adrian, regarding your recommendation to use "80% or less" alcohol, 80% in what? Water? Not a good idea. Some other solvent?? In the US, what is sold as "denatured alcohol" can have quite a range of ethanol content, and the 'denaturants' can vary in chemical identity and amount as well. Some brands have a pretty high concentration of methanol, others not as much. What you are able to buy in Slovakia may be considerably different. If your Eastern European manufacturers add some other solvent, I would want to know what it is before casually using it.

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    Registered User Keith Newell's Avatar
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    Default Re: How to identify lacquer vs. varnish finish?

    I have seen an oil varnish get softened by denatured alcohol but will have to double check on a peice I have here.
    Keith
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    Default Re: How to identify lacquer vs. varnish finish?

    I have had a sample block of walnut sprayed with Behlen's Rockhard TableTop Varnish sitting arount the shop for about a year. Just now wiped it vigorously with denatured alcohol for >30 seconds. Upon evaporation, the film did not feel tacky, and appeared to be unfazed by the solvent. The other side of the block was FP'd (shellac) to fill the pores. Upon wiping that side, the surface immediately felt tacky. After Keith's post, it is a relief to find that, at least for me, the chemistry is what it is supposed to be.

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    Adrian Minarovic
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    Default Re: How to identify lacquer vs. varnish finish?

    I finished that mandolin with modern alkyd-urethane oil varnish and french polished it. It's two years old and after application of spirit varnish (basicly shellac in 98.5% ethanol grain alcohol- contains 0.3% naphtha as denaturant and the rest is water or GOK) and the whole layer softens - becomes rubbery. It doesn't dissolve (the FP goes away in second) but you can damage it by very gentle pressure. After complete evaporation of alcohol the varnish layer is back to its original consistency. Maybe some brands of oil varnishes are somewhat suspectible to ethanol. May be that the alcohol goes through the oil varnish and softens the shellac sealer underneath.
    The terminology is different here so excuse me. In our country alcohol is always ethanol in general speach - methanol and other alcohols are virtually never used and perhaps prohibited in publicly available products. I usually bought 60 or 80% alcohol in pharmacy so that would be 80% ethanol and 20% water, or I could buy 95% denatured with naphtha. The denatured alcohol I use now is most concentrated fuel for chimneyless fireplaces. Completely dissolves 1/32" thick shellac flakes in minutes, great stuff. And doesn't smelll bad at all. That's why I recommended lower percentage, you don't want to do too much damage with your test even on invisible spot.
    I agree about pre-loar (and perhaps all lower models) were spirit varnish.
    Adrian

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    Default Re: How to identify lacquer vs. varnish finish?

    WARNING - ridiculously long reply ...

    The term "varnish" has really become useless. At a recent festival in VA, John Hamlett and I looked a a very nice D-18 copy made by a local builder. We complimented his fine work, and I asked what the finish was. He said it was "varnish". Later, on his website, I found that his "varnish" was "conversion varnish", a general trade name for a catalyzed polyurethane finish. It looked great, and sounded great, and I wouldn't say anything negative about the finish except that catalyzed poly finishes don't "age" in the sense that traditional varnish or nitro lacquer does, and it's difficult (maybe impossible?) to repair.

    The V word has been marketed as a tonally superior finish to lacquer, and personally I'm not sure that it's true, but in this instance I think it's maybe a bit misleading. Whatever, it was a fine guitar, and Taylor, Bourgeois, Ovation and many others use these finishes due to their obvious advantages for production.

    In the violin world, oil varnish refers to finishes based on linseed or other natural oils that dry largely by polymerization. Spirit varnish refers to alcohol/shellac-based finishes that dry through solvent evaporation. Modern commercial alkyd varnishes do not use natural oils (Others please correct me if I'm wrong). Oil varnish finishes tend to be softer and thicker than spirit varnish finishes, and are generally preferred on violins, probably because this is what the Cremona masters used rather than due to some tonal advantage. But this point has been argued to death. Would Stradivari have used catalyzed poly or alkyd varnish if he could have? I think he might have, along with his new CNC router. But there have been so many varnish formulations over so many years, and so much discussion and contradiction that it's not always clear what's actually in a varnish and so not straightforward to determine what will dissolve what and to learn much about a finish by applying solvents.

    My experience is:
    * ethanol (grain alcohol) will not have much effect on nitro lacquer. I'm not sure what all is used to "denature" the alcohol that you buy at the hardware store but denatured alcohol may be more aggressive as a solvent of lacquer.
    * ethanol can be used, with a rag and elbow grease, to completely remove a spirit varnish finish.
    * ethanol ~may~ affect a linseed oil based finish, but not as aggressively as a spirit varnish.
    * shellac will dissolve in ethanol, but an old shellac finish can be more resistant to any solvent than a newer one.
    * naptha can be used to clean oil or spirit violin finishes, and will attack the finish but not strongly
    * acetone, butyl cellosolve, lacquer thinner, and CA glue will affect nitro lacquer quickly
    * nothing much but a heat gun can remove or affect catalyzed poly "varnishes". Maybe methylene chloride strippers will affect them. Anybody know?

    But back to the original question...I think most finishes can be differentiated visually, though lacquer is not easily distinguished from the catalyzed poly on a new instrument. I can tell a spirit varnish from an oil varnish on a violin. For one thing, oil tends not to check at all, where spirit finishes get a very fine cross checking over time. But it's not a hard and fast rule. Spirit varnishes tend to appear hard and glossy, and may flake. Oil varnish, applied over a spirit base, is a good way to get finish crazing.

    Lacquer tends to look hard and smooth, and can be thin or thick, but typically glossy. The weather checking that you see on old instruments is an easy marker for nitro lacquer. As many instruments a you've seen, Charles, I'm sure you have a feel for all of this. But the visual cues are not always reliable for identification, just as an informed guess. Which is why Charles asked in the first place. Get out the solvents.

    I admit to a morbid fascination about this topic, why I'm so wordy in this reply, because it is so difficult to sort out the advantages and disadvantages, claims and counter-claims, and the ideas that become doctrine among those of us who love stringed things. From a practical standpoint, as a repairer, you need to be able to do it all to the extent possible. As a builder, you can choose the finish you like and roll with it.

    I'm open to any and all corrections to what I've said here. Bring it.
    Jack C.
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    Registered User Vernon Hughes's Avatar
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    Default Re: How to identify lacquer vs. varnish finish?

    I hijacked this picture off an old thread a long time ago as to which finish gibson used way back when..If I remember correctly,this was a picture of the finish as remembered by an old gibson employee.
    Click image for larger version. 

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    Hughes F-5 #1
    Hughes A model #1
    1922 Gibson A-2
    1958 Gibson A-5
    1924 Gibson snakehead A Blackface

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    Default Re: How to identify lacquer vs. varnish finish?

    I remember (and "borrowed") that picture too. As I remember, Bill Halsey asked the guy in the paint/hardware store where Gibson bought or might have bought stuff if he remembered what varnish Gibson used, and he set that can on the counter.

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    Default Re: How to identify lacquer vs. varnish finish?

    Quote Originally Posted by jackc View Post
    WARNING - ridiculously long reply ...
    An exceptional response.
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    Default Re: How to identify lacquer vs. varnish finish?

    R.M. Mottola wrote an article on denatured alcohols within the last year or so in American Lutherie. The composition varies widely from brand to brand. A few are ~90% ethanol, with the remainder denaturants and water. Other brands may be as little as ~40% ethanol, with large amounts of methanol and other polar organics (mostly alcohols and ethers or esters, depending on what is currently cheap). Five percent of any ethanol or denatured ethanol will always be water, as "absolute" ethanol is hygroscopic and quickly absorbs water until a 95% ethanol/5% water azeotropic mixture is formed. The 5% water cannot be distilled from the azeotropic mixture (or from any azeotropic mixture, for that matter), but must be chemically purged, which is very expensive. You have to do things like distilling the ethanol over phosphoric anhydride, which is nasty and dangerous. Plus, you then have to separate out the phosphoric acid which is formed.

    I use "Klean Strip Green" denatured alcohol, which is one of the brands containing 90% or (slightly) more ethanol, as it is available in a local big box hardware store. However, I have used other brands with high methanol content with very similar results. As I stated earlier, ethanol and other alcohols will attack NC lacquer, albeit slowly. Slightly higher molar mass alcohols are a component of lacquer thinners/solvents. They attack NC lacquer very slowly compared to the other components in the mixture, but they will do so. One useful benefit of that is that if a chip comes loose at the edge of a finished area, you can wick a small amount of alcohol under the chip, press it to the surface, and it will re-adhere. The alcohol softens the inner surface just enough to briefly produce some tack and cause the lacquer film to stick to the surface. Comes in handy when reaming holes in headstocks. The finish film around the hole is sometimes loosened by the reaming process, no matter how much care is taken. A drop of alcohol touched to the edge of the hole wicks in under the film and causes it to stick to the surface again. If you tried the same thing with lacquer thinner, you would get the film to stick alright, but you would also have a softened mess that would have to outgas for days to weeks before it could be leveled again.

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