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UV cure of shellac?

1/4/17       
Brian Burns  Member

Website: lessonsinlutherie.com

Hello All,

Some 50 years ago I built an ultraviolet drying cabinet for an oil violin varnish that I was making. It worked like a champ on the linseed oil based finish, but that soft coating killed the treble response of three classical guitars before I realized that I should be using the traditional hard finish, shellac.

Having spent a couple of days looking for info on UV "sun tanning" of wood to darken its color, I remembered my UV drying box. Has anyone tried using UV to speed up shellac's long cure time?

Cheers,

Brian Burns

1/4/17       #2: UV cure of shellac? ...
MichaelH

Website: http://properwoodfinishing.com

Different mechanics as with a traditional U.V. cure finish. The alcohol in the shellac makes it a fast dry, solvent release finish. Heat will help providing that you do not hit it with to much where it will skin the top over and cause you solvent pop. Any cheap automotive paint jobber can sell you a quartz heater that is adjustable to the work surface.

1/5/17       #3: UV cure of shellac? ...
RobertJ

My wife has her nails done with Shellac, and it cures under a UV light box.

Can you find one to fit a Violin????

1/5/17       #4: UV cure of shellac? ...
Brian Burns  Member

Website: lessonsinlutherie.com

Hello Michael and Robert,

Michael I do use moderate heat, and keep the air moving to speed the cure of my shellac. In my googling around I ran across a number of sites that use UV for drying shellac on fingernails, as Robert mentions, and I thought that perhaps someone had tried it on a larger scale.

According to a local expert on finishing---he studied finishing to be a museum curator---shellac takes a lot longer than most people think to cure up hard. Over a long period of years it cross links, and is no longer soluable in alcohol, and I wouldn't want to speed up that process!

Robert, received wisdom is that an oil varnish is the best finish for a fine violin, because it damps out some of the high frequency screechiness. For a plucked instrument like a guitar that's bad, hence the use of shellac, at least on the soundboard.

The best source of UV info I found was Solacure. I had a long conversation with the owner---an electric guitar enthusiast. He has a UV kit for drying oil varnish on a violin in a day instead of a week. I know that is accurate, as I did it myself back in the early 1960's.

Cheers,

Brian

http://www.solacure.com

1/5/17       #5: UV cure of shellac? ...
Rick Mosher

I worked with UV finishes and they are very popular with the guitar making community. As well as floor finishes and architectural millwork.
Most of the places I have checked out are using a polyester system. The finish is made by adding an activator to the original finish, not all finishes can be changed. You need to check that out with a supplier. I was amazed at the speed of such a system, I could do a fully filled, fully cured and buffed piece in one day!

The equipment to do the finish is pretty expensive but the results are amazing. You can buy cheaper curing lights but they are not the way to go. Google guitars and UV curing and you will see several companies using them. Write them an email I am sure they will be helpful, the Luthier forums are good as well.

Luthier Tips du Jour

1/5/17       #6: UV cure of shellac? ...
Brian Burns  Member

Website: lessonsinlutherie.com

Hello Rick,

Thanks for the response!

I make traditional Spanish classical and flamenco guitars which are particularly sensitive to the type and quantity of finish that is used on them. We nylon string (formerly gut string) guitar builders are always struggling to conserve treble response, because the nylon strings don't give us much high frequency sound power to work with.

French polished shellac will build up a nice gloss at a couple of mils thick, and most importantly, it is quite hard and low in acoustic damping. It's not very durable, though better than shellac's reputation would indicate, provided that you use de-waxed. We put up with its lack of durability in exchange for the improvement in tone quality and responsiveness of the guitar. It's readily repairable as it's 100% burn-back.

Ervin Somogyi, one of the best steel string builders alive, has his guitars French polished, and says that even steel string instruments sound better when finished with shellac.

Cheers,

Brian

1/5/17       #7: UV cure of shellac? ...
Rick Mosher

I don't build guitars so I can't tell you what is best or not. I have made it my business to never believe anything anyone says until I have tried it myself. I particularly like doing the "impossible."

I suggest giving it a try and see for yourself if it works or not. There are a lot of custom guitar makers using it and I'm sure they are all concerned about the sound as well.

This could be your chance to show Ervin Somogyi a new trick. :)


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