finish questions

[fatdaddypreacher]

having been asked something yesterday that i have been curious about for years, i thought this may be the best place to get counsel. what is the difference between shellac and varnish. what are instances when they would be a preferred finish over more modern products. i thought some first hand experience all wadded up in one place would be better than exploring the net...which i don't do well at all.

thanks.

 

[tnt423]

Very barebones and my memory is not perfect.

Shellac is a by-product of the Lac Beetle and is harvested in India and refined into buttons or flakes that dissolve in alcohol. It is primarily an evaporative finish that will remelt and is somewhat fragile. I have found this to be great for sealing as almost any finish will stick to it and it can be used between two somewhat incompatible finishes.

Varnish was originally amber ground into powder and dissolved in different spirits including alcohol, turps and mineral spirits. Varnish making was for centuries very closely guarded and many formulas have been lost to failing memories or untimely deaths. Modern varnishes are usually poly blends (is that redundant?) that cure in steps. First they evaporate off the suspension thinner, then they combine or cross-link into long chains of molecules that harden over time. Until the molecules link the layers will blend into each other somewhat and after it has cured the finish will build into separate layers. This can be seen by witness lines that look like topographical maps when layers are revealed when leveling the finish. I onlu use modern varnishes on furniture as the only time I tried it on a guitar I was not happy with the outcome and asked for the instrument back after about a year to strip and refin. I do like using spirit varnish when repairing violins.

People spend a lifetime in the study of finishes and application techniques so this quick explanation doesn't begin to scratch the surface.
Hope it helps though.

 

[fatdaddypreacher]

thanks tnt...most informative
have you tried modern 'cab-acrlyic' lacquers on instrument builds?, or is this one of those you were not happy with. with my limited experience with them, and no experience with nitro, they seem to be user friendly and can furnish polished, clear finishes. wouldn't be good for the 'purist' who are building vintage pieces, but curious about them also. any experience you care to share?

thanks again

 

[tnt423]

Lacquers are a whole study in themselves. They are not varnishes.

The Japanese, who invented lacquer, use a very toxic tree extract that is totally different from nitro, I think they call it Urisho, forgive me if my spelling is wrong or I am calling it incorrectly. Its been a long while since I've done study on this.

Nitrocellulose is based on cotton fibers and chemically altered to let it form a clear film. It's almost unobtainable in pure form and I do not recommend attempting to formulate it on your own, very hazardous. Modern lacquers are blends with some nitro added, but not quite the same as what was available in the 1920-1950s. Most have acrylics as the main solids content. Pure acrylics are more difficult to repair after a year or so. Neither every fully cure and in my opinion continue to shrink forever. Most shrinkage occurs in the first month or so. If attempting repairs have the customer bring the instrument back in three months and build more in necessary.

I have used acrylic and water-borne, I like them but as you said "purists" don't seem to accept them. I had trouble with burn in (coats blending) with the water-borne, but I hear they are much better now. If they work like varnishes repair and touch up becomes very difficult to do without visible evidence. If I ever get caught up with custom builds I intend to explore them further.

Personally, I cannot hear a difference between a thinly applied lacquer and thin poly finish on a solid body guitar. I can hear the difference on a fine acoustic, but which is better is wholly subjective. But YMMV.

I am going strictly off memory here so I may be mistaken. If I was buidling for myself right now I would try the Lovoc from Sherwin-Williams, mostly because the store by the shop has it in stock in gallons. But on personal build I take chances with full knowledge that I may have to strip and redo.

 

[fatdaddypreacher]

i will have 3, possibly four lp style builds ready for finishing shortly, plus one smaller solid body similar to a telecaster. i have some behlen 'nitro' and i decided to get some cab acrlyic lacquer like we use at work building custom furniture. i intend to do both and see if i can realize any differences to speak of. will also make them available to my 'players' to see what they think.

once again, thanks for the help

 

[tnt423]

Let me know what they say, I'm always interested in learning more.
Will you tell them which guitar has what finish before they play them?

 

[fatdaddypreacher]

wasn't planning on it...i'm devious that way. will be a while, but will post results.

thanks again