To relacquer or leave original
From time to time questions and discussions arise on the topic of lacquer. What kind of lacquer did Conn use? What exactly is "Lustre-Conn" lacquer, really? And last but not least: Should a vintage Conn, or any other vintage brass instrument, be relacquered or not? Recently (October/November 2005) there have been some interesting discussions related to these topics on the Trumpet Herald Forum. What follows is for the most part an extract of posts from there (with special thanks to Rusty Russell).
Types of lacquer
Modern lacquer, that is most lacquer since the late 1980's, is either epoxy, acrylic or polyurethane (perhaps that is the same thing?). Before the late 1980's, most lacquer was nitro-cellulose. The nitro cellulose has been illegal since the late 1980's and the epoxy, acrylic and polyurethane lacquers have been introduced.
Acoustic quality of different lacquer types
Rusty Russell: "There's a huge difference in the way these finishes sound, feel, and age. In the guitar industry, replacing original nitro-cellulose lacquer with a more modern finish will typically lower the value of a vintage instrument by half, largely because of the effect on tone. While not quite as critical with horns, it is still a factor.
Any time you coat a surface with a hard-drying liquid, the resonant properties of the underlying surface will be affected. Nitro-cellulose has certain properties that make these effects positive; it can be applied in very thin coats, and as it ages, it becomes more fragile, more crystaline, kind of collapses into itself. Chemist may be able to give the technical lowdown on this, but somehow nitro-cellulose "breathes" to some degree after a few years, and most believe it has a very limited effect on the underlying surface (in terms of resonance). A piece of wood with a nice, thin coat of nitro-cellulose will still expand a little when the humidity is high and contract when it's low. Coatings like polyurethane, on the other hand, are like a hard candy shell. The under-surface is hermetically sealed, the stuff doesn't breathe at all. Polyurethane also retains its original "set." Dries hard, stays hard; dries "rubbery," stays that way. My first experience with this was as a guitarist and repairman. I stripped a good-sounding Telecaster body & refinished it with the latest/greatest (according to the paint industry, which always touts its durability) polyurethane finish, and the guitar sounded awful when re-assembled. I cast around for answers, and was hipped to the nitro-cellulose thing. Stripped it again, found a source for nitro, and re-finished. Sounded killer.
There are no doubt people out there who actually like what a modern, harder finish sounds like. My experience with horns is that these sprays attenuate the lowest and highest parts of the spectrum. To me this sounds lifeless. I have stripped a late 1990's "lacquer" Bach Stradivarius (polyurethane) and re-sprayed it with elicit nitro-cellulose. The difference blew everyone away."
Robert Rowe says that the "comment that nitro-cellulose lacquer is "illicit" or "illegal" is not correct. Nitro-cellulose lacquer can still be purchased legally. The handling and disposition of the material is regulated, by the E.P.A. (Environmental Protection Agency) and OSHA (Office for Safety and Hazards Administration)."
So, what is Lustre-Conn? Conn started using, or at least advertising, Lustre-Conn in 1957, so it is safe to assume that most Conn brass instruments produced from 1957 on have a Lustre-Conn finish. It is very resistant to wear and tear. I personnaly played a 1964 Conn 15B Director for almost 25 years and there isn't even a hint of wear in the spots where I hold the instrument. We know it is a nitro-cellulose lacquer (which is good, based on the above), but beyond that we don't know what it is. As far as is known, nobody has been able to duplicate Lustre-Conn; it is a "lost art". Pre-1957 Conn instruments are also lacquered with a nitro-cellulose lacquer. Whether, and if so to what extent, it is different from Lustre-Conn, I don't know. I suspect it is, since the lacquer on pre-1957 Conn instruments tends to get "sunburn": it turns dark with exposure to ultra violet light (the sun). This doesn't affect the quality of the lacquer at all as far as I can tell, just the color of it.
Different people have a different threshold for accepting lacquer wear and discoloration. Relacquering an instrument will make it look "like new" again, although it has proven to be extremely difficult or even impossible to replicate the hue of original Conn lacquer, be it Lustre-Conn or the pre-1957 lacquer (aside: the hue of the lacquer is one of the ways of telling if a Conn has been relacquered. Especially easy to tell on instruments with a Coprion bell). As for monetary value of an instrument, and speaking strictly for myself, I avoid relacquered instruments preferring those with original lacquer. Yes, preferably original lacquer in decent condition. Given the choice between two identical instruments, one nicely relacquered, the other with so-so original lacquer I will choose the one with the original lacquer. Monetary value: in my opinion relacquering an instrument with original lacquer does cut its value by one-third to one-half, even over one with so-so original lacquer. The "sound" issue has of course been extensively addressed above. Another hazard with relacquering I would like to touch upon is that the process involves polishing the instrument. If this isn't done carefully, the original engraving will become fainter or even lost completely due to the metal becoming thinner with the polishing. This thinner metal might of course well also have an affect on the sound. In the end though, the choice is up to the owner of the instrument.