CONVERSION VARNISH AND NITRO DIFFERENCES

[jingle_jangle]

Here's a question from Gene Schillacci:

"Paul,
This is probably one question for a thread of its own, but I'd like to know more about the differences between conversion varnish (or whatever modern Rickenbackers are finished with) and the Nitrocellulose finishes of old and reissue Fenders and Gibsons. The Rick finish is much thicker, but on my 1993 4001v63, which has seen a lot of playing time, the finish is still nearly perfect. Only a few places around the frets has it chipped off or worn noticeably. The chrome on the horseshoe is really worn, but the finish just keeps going and going!"

So, here's the new thread!

Well, yeah, Gene, it's really apples and oranges.

Most briefly, nitrocellulose and its compatriots enamels and acrylic lacquers, dry by solvent evaporation. Conversion varnish and its compatriots polyester lacquer and epoxy enamel, all cure by the reaction known as catalyzation.

That's the main distinction between these types of finishes.

Years and even centuries ago, the finishes available were true lacquers (from insects and tree sap), which was the preferred finish in the Far East for precious objects made of wood and paper, shellacs, and varnishes, for objects like violins and other stringed instruments.

Modern chemistry gives us the catalyzing type of finish, which includes conversion varnishes. This type of finish came about in answer to a need for a durable finish which allowed a greater film thickness along with accelerated hardening times to facilitate production.

Nitrocellulose--which RIC used until sometime in 1959--was the finish of choice for electric stringed instrument makers back then. It remains so because of a common misperception that in all cases, a thin finish is a better finish. This is certainly true of acoustic guitars, which operate on the principle of enclosing and controlling a volume of air within a case of wood. The less finish, the better from the standpoint of vibration transmission at least.

The less air enclosed by an electric guitar body, the less important the thickness of finish becomes. I do not hold with there being a huge sonic difference between a solid-bodied guitar or bass finished with .002" of nitro, vs. the same instrument finished with .010" of polyester layered upon itself for ease of gloss and durability. There will be a difference, depending upon how sensitive the pickups are, as they remain the primary determinant of the sound of a solid-bodied instrument, in my experience.

In the older days, before self-catalyzing coatings came onto the finishing scene, air-dried lacquers were the easiest way to protect wood, with a finish that dried dust-free in a relatively short time compared to enamels and alkyd varnishes and offered sup[erior protection to shellacs, which have poor water and chemical resistance.

But although nitro is easy to spray and sets up dust-free in a short time, its "hang time" (the time an instrument must hang, undisturbed, before buffing and final assembly and setup) is rather long and can extend to weeks depending on film thickness and environmental factors.

Enter CV, which catalyzes through the entire film thickness, instead of outside-in, and allows the buildup of thicker films with a good deal more resilience than nitro, and better protection to boot. No doubt it was quicker cycle times, the ability to color-sand and buff to a glasslike surface within a couple of days, and a fraction of the old hang-times, that caused RIC to switch from nitro to CV back almost 50 years ago.

[gavin]

Paul,

Once again, you are the head guru in the luthiers arena.

[kenposurf]

Yep...think Paul is right about finish thickness and how it relates to tone of a solidbody when amped...I have a couple of guitars with the very thinnest spray of nitro possible...really does transmit string vibration much more..but..when amped I can't tell the difference between it and my guitars that have a thick poly finish..sounds good in front of the TV whilst sitting out the sofa though..

[squirebass]

Wow, so Rickenbacker stopped using nitro in 1959?!? I coulda sworn that my '71 and '73 basses were finished with nitro. They have a much thinner looking finish that any of the ones I've purchased in the '90s and '00s. I know the Rickenbacker finishing process is a trade secret, but is CV what my '71 and '73 have on them? And thanks for the info, Paul, very informative!

[jingle_jangle]

Gene, the conversion varnish formula that Electro String and later RIC, has used over the years, along with their application methods and specs, have changed many times since 1959.

The finishing process has been described as a "trade secret" in older literature, but recently, with a lot of photos having been published by folks who've taken the factory tours at RIC75, the general process has seen the light of day, although details are still closely-guarded.

The factory finishes on your '71 and '73 were CV. As I pointed out, CV is glass-smooth when it leaves the factory, but shrinks quite a bit as it ages. Within a few months of finishing, the film thickness will be at its final dimension and a bit of woodgrain can be evident. Older Ricks have a very thin film of CV, generally under .005" in my experience.

[squirebass]

Thanks Paul for the explanation. I have wondered about the differences for years and it is good to have someone who really knows the stuff tell us about it. I've had a few folks give me their take and it never made much sense, probably because they didn't really know that much about it. CV must be really tough, because I have banged my v63 around a few times and thought I would definitely have a bad ding in the finish, but then it polished right out. To this day, that bass looks near mint and it has been played out a lot! And I really wish I hadn't missed the RIC 75th Anniversary, I would have enjoyed taking the factory tour.