Removing oil from French Polishing

[Mike Perez]

I have been making various test sample to see which finish I will use on a guitar repair/refinish. One finish is blonde flake shellac.
The surface was becoming rough, so I added a few drops of olive oil to the pad and it really helped smooth the finish and it came out great
Half of the shellac test sample is going to have Crystalac on top of shellac I am wondering how do I remove traces of the oil from the shellac to brush on Crystalac on the shellac?
I have read about using only alcohol on a fresh pad to wipe off the remaining oil or even using naphtha to remove the traces of oil.
Thank you for any advice,
Mike

[Alan Carruth]

Alcohol is the traditional solvent for that. It's a sort of catch-22; the oil is there to keep the pad from sticking to the soft shellac. Putting alcohol on the pad tends to soften the shellac more and make it stick. At the same time, non-drying vegetable oils are attracted to alcohol, so alcohol on the pad will pick up the oil. If you don't pick up a non-drying oil it is attracted to whatever alcohol is still in the shellac on the surface, and forms a film on the surface that tends to lock it in, so the surface stays soft. Sometimes for months... Once the shellac hardens enough you can sand it back to get the oil off the surface.

If you don't want to do that there are several solutions I know of. One is to start with a pad cover that has no oil in it, and use a small amount of alcohol the pick up the oil on the surface. The trick is to use just enough pressure on the pad to stay in contact, but not enough to make the pad stick. As you remove the oil and allow the pad to get drier it's less likely to stick to the harder shellac. Eventually, in theory, all of the oil ends up in the pad just as the alcohol all dries out, and you have a hard, smooth surface. This is the essential skill of French polishing, and can take time to develop.

You can use a drying oil, such as raw linseed oil or walnut oil, which will be thinner than boiled/treated oil. This has a tendency to combine chemically with the shellac resin, rendering it a little less soluble and tougher, but it also seems to be more likely to shrink over time, and the surface is not as 'wet' looking as with olive oil. The oil hardens via an oxidation/polymerization reaction, and when it does it's no longer 'oil' and doesn't lock up the alcohol in the surface, so it can dry.

You can use a different solvent, such as naphtha. This could be a mix of different hydrocarbons. Be sure there's nothing in it that will mess up the shellac.

I'd be wary of putting Crystalac over a coat of shellac. There's an old painter's rule: 'fat over lean': never put a less flexible coating over a softer one. The under layer moves, and the top coat can't move with it, so it cracks. That's how they get 'antiqued' crackle finishes. A lot depends on how thick the under layer is; a light wash that only seals the wood from penetration of the final coating probably won't cause problems. In that case all you may need to to is wipe on a wash of shellac with a rag. If this is going to be some sort of sunburst or color coat for the lacquer I'd test it out on scrap to be sure the seal coat is adequate to keep color out of the end grain of the wood. I would avoid putting a coating of lacquer over a smooth French polished surface unless it was well sanded back to the wood, so the shellac is only filling pores.

[Mike Perez]

Thank you for that information.
I did end up applying many coats of shellac and it came out fantastic, but applying Crystalac on top of such a thick coat of shellac might not be the best move. That advice about a harder finish on a flexible finish is advice I will heed.
I'll make another test piece with just a light seal coat of shellac with no oi. The shellac was the nicest finish of all.
It brought such an amazing luster to the mahogany. I used a contrasting dark brown pore filler and amber stain under the shellac.
The Crystalac is simply to provide a more protective finish than the shellac.
The other finish that was closest to the blonde shellac in its appearance was Tru Oil but it was not close to the blonde shellac.
If I could get the shellac look with a more protective finish, it would be ideal.

[Pat Foster]

Not the traditional way, but you can eliminate oil altogether. Learned that from Cyndy Burton, who does the FP for Jeffrey Elliott's guitars.

[Mike Perez]

I didn't use the olive oil until the very end. It was starting to stick and that was causing it to wrinkle the finish.
If I were going for just a shellac finish, the smooth "oily feel" would be ideal.
It's a shame it isn't tougher. It is a great looking finish.

[Alan Carruth]

The nice thing about French polish is that once you know how to do it it's easy to renew. Shellac also gets tougher and less soluble with age, unlike nitro.

I have used oil-resin varnishes for years. IMO they look even better than shellac, and hold up better over time. The main down side is that they can take a lot of time to apply and rub up. Another is that it can be hard to find a good one that will harden reliably on some of the tropical woods. It also often seems that just when I've found one that works well, and gotten good at working with it, it gets discontinued by the maker. It's possible to make your own: I've done it, and would not bother to again except out of curiosity.

[Mike Perez]

What are some recommended oil-resin varnishes?

[Alan Carruth]

I've been using Murdoch's 'Ure-alkyd 500' floor varnish for a few years. It's a bit finicky about drying on some tropical woods, although UV light usually helps. I order it directly from Sutherland-Welles, the maker, in Vermont. It's quite hard. For something softer many makers report good results with Pratt & Lambert #38, which I believe you can get at Sherwin-Williams stores.

[Mike Perez]

I wiped the shellac surface twice with a clean cloth with naptha. Each time with a fresh piece. The surface is incredibly smooth and even feels "slick," not sticky at all. Does that mean some oil remains? Thank you.