Questions about application of oil varnish

[Jacob Hagerty]

Hello, I am just nearing the end of my first build from scratch. I built 2 mandolin kits previous to this one.(pics below) First being from International Violin Company, second from StewMac.
Both I finished with spray can lacquer from StewMac, worked fine but would like something more natural.

I found an oil varnish recipe from 1704 which includes products like Gum Sandarac, Gum Mastic, Seedlac and spike lavender oil.

I purchased some blond shellac flakes previous to finding this recipe and dissolved it in denatured alcohol and attempted to build coats and French polish on some scrap I had laying around, came out pretty nice.

Has anyone here ever used just straight shellac for a finish?

Has anyone here used the products mentioned above?

I don't have a spray rig so I will be attempting to apply this finish by hand....any tips?

Should I seal in the hand rubbed sunburst somehow before hand applying the oil varnish?

Should I brush on the varnish or apply with my pad?

How long do I let it dry before level sanding?

Any other tips and tricks?

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[rcc56]

Straight shellac was often used for finishes. Sometimes, sandarac was added to the shellac. It gives the shellac more body. It also slows drying.

If you try to build a straight shellac finish too thickly, it will become cloudy, no matter how careful you are. French polished finishes are thinner than lacquer or oil varnish finishes.

Denatured alcohol can cause color changes and drying problems. I found this out the hard way. Always use pure grain alcohol, whether you are using it for dyes or making shellac. I've had stained wood surfaces turn green when I applied shellac made with denatured alcohol over it.

Oil varnishes are usually brushed on. Allow at least two or three days between coats and scuff sand with 320 before re-coating. The varnish may need to be thinned slightly to make it easier to apply.

Generally, violin people seal the wood before applying oil varnish. Some of the violin houses sell sizing made for the job. 3 centuries ago, albumen [egg white] was often used for a sealer. I have applied oil varnish over a thin shellac sealer, but I don't know if that would work over stained wood-- it might disrupt the colored surface.

If you do try a thin shellac sealer, make a trial run on a test board. Make sure the stain is thoroughly dry, make one pass only with the shellac, wait a couple of hours, and repeat a couple of times until the stain is sealed well enough to allow for a more liberal coating. If I was to try this on a sunbursted wood surface, I would start in the middle and work my way outwards, moving only from light to dark.

The best places for info on oil varnish are the accepted violin building texts.

I have used French polished shellac for a top coating over store-bought [from a violin supplier] oil varnish with success. The shellac maintains a higher gloss than oil varnish.

[Jacob Hagerty]

wonderful information. Thank you!

[peter.coombe]

Yes and yes.

Firstly the 1704 varnish is a spirit varnish, not an oil varnish (i.e. it dissolves in alcohol). It uses seedlac, not shellac, but shellac should work fine. The addition of the other resins changes the qualities a bit from pure shellac, and I do slightly prefer it over shellac, although shellac works fine. I brush on 2 or 3 coats of shellac before French polishing. As for the stain, it depends on what sort of stain you have used. If you used water soluble analine dyes then you most likely won't have any problem brushing on shellac or 1704. If you used alcohol soluble dye then you may have some problems. I have always used water soluble analine dyes. How long to let the brushed on coats dry? An hour should be enough before you start French polishing. French polishing is an art in itself and practice makes perfect, but once you have the technique down the quality of the finish can be superb. Just look at Gilchrist's finishes.

[tom.gibson]

The 1704 varnish is actually a spirit varnish, not an oil varnish. Because it dries fast it is tricky to apply, needing a good quality brush, long straight overlapping strokes, and no going back to fix up mistakes and brush marks. After final flattening, a top coat of shellac would probably leave the best finish. Straight shellac is a great finish, and not as difficult, IMO, as all the mystique around French polishing would have you believe. There's a heap of information on French polishing on the web.

As for oil varnish, you could use a violin varnish or spar varnish and apply with a brush, or even your hand. Controlling dust can be a problem.

[Geoff B]

Whenever I've tried rubbing or brushing any finish over a dyed wood surface (whether water or alcohol based dye) it picks up a bunch of color and even moves it around some. Could be I wasn't doing it right, but it's incredibly frustrating in my experience.

My solution has been to spray 1 or 2 very light coats of shellac to seal the colors in. Not even enough to get a luster on the surface. Scraping binding with just this littler amount of finish is easier too.
Then I build whatever finish (shellac, oil varnish or tru-oil (I've heard arguments over what it is exactly, but it's worked the best for me and gets that deep glow really well)). Once the finish is built up, I level sand and french polish with straight shellac. It may not be glorious or mysterious but it's worked for me and shellac is protective enough if you treat it well, and shows character nicely if you like that and is so easy to touch up too if you ever want to.
The use of egg whites to seal tops still seems like a thing, especially with classical guitar builders I've known. I've never tried it but have been curious.