French polishing

Construction and repair of Classical Guitar and related instruments
SteveL123
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Joined: Thu Feb 09, 2017 5:05 pm

French polishing

Post by SteveL123 » Sun Apr 07, 2019 8:01 pm

Is the following a reasonable procedure for French polishing? Are the cuts used (dilution) ok?


-Bodying: shellac dilution 12%. A lot of coats, one every 30 minutes. It is not important this phase; the final result is to create a sufficient thickness to be sanded with very fine sandpaper without touching wood. Allow to dry a couple of days.

- Sanding with 1000 wet sandpaper. The final result is to remove all undulations and imperfections of shellac.

- Glazing: shellac dilution from 7%. 2 or 3 coats every 12 hours. In this phase it is essential to use sufficient oil so that the pad can flow without friction. YOU NEED TO PUSH (without to break guitar!). In this phase you have to drag the shellac, not to add it. Allow to dry 12 hours.

- 1 coat only alcool. CAUTION: the pad has to be a little moist, not wet! Allow to dry 12 hours.

-Last coat shellac 2,5%. Not circular movements but only straight movements. Allow to dry at least 2 days.

-POLISH.

12% dilution would be 48 grams shellac + 400 ml alcohol
(48/400= 0.12= 12%)
That would make it a 1 lb cut I think.

ChristianSchwengeler
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Location: Lisbon Portugal

Re: French polishing

Post by ChristianSchwengeler » Sun Apr 07, 2019 8:43 pm

I only do french polish on the sound board.

I make first 2 or 3 washcoats before starting bodying, but rather with a 2 pound cut, and sometimes I even apply the washcoats with a brush. After drying I do level sand them with fine sanding pads. It is easier then to have smoother bodying sessions and less bodying necessary. My experience is that it is no use to make things more complicated than they really are.

When bodying I wait 1 hour betwen sessions and aply max 4 sessions and then let gaz out for 18 hours at least, then level sanding again before the enxt 4 bodying sessions. For bodying I use also a stronger cut about 1 1/2 pound gallon. Sanding is tricky and it depends a lot of what you use, I use fine automotive sanding pads.

Anyway it depends what you are trying to achieve, personally I hate high gloss finish and in this case my pocedure is satisfying.

On the other hand I use 10% sandarac, 10% benzoe and 10% mastix together with 70 % dewaxed shellack flakes, this blend is easier to work with and you need very little oil only or only for glazing.

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James Lister
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Re: French polishing

Post by James Lister » Mon Apr 08, 2019 9:00 am

I'm curious as to where you got that procedure. It might work, but I wouldn't describe it as French polishing. A 1 lb cut is fine. You can build up quicker with a stronger cut, but it's more difficult.

The idea that you can apply one coat every 30 minutes suggests to me that the method involves using a quite wet rubber, doing one pass over the whole surface, not worrying about getting it flat, and then repeating. This is not French polishing - it's just applying shellac. Although it can work, getting a smooth even finish by sanding back a rough surface is difficult. There's always a risk of rubbing through to the wood, and the finish is likely to be patchy. This will be particularly noticeable if you're using anything other than a blonde shellac.

The method I was taught (and what I believe to be the traditional method), is to apply the shellac with a relatively dry pad, so that there are no "undulations" that need sanding out. I talk about polishing "sessions" rather than coats. Two sessions are the most you're likely to do in one day - with only one session per day after the first few days. Each session will last about 45 minutes initially, and more like 25 minutes in the later stages (less time for each session when you have less experience, a bit more if you're using oil). Minimal sanding (if any) between sessions, and shouldn't need more than a light sanding before the final session (glazing) to get it perfectly flat. Glazing session I use a really weak mix, and some oil.

I've never understood the need to "push" down on the guitar during polishing. Risky on the top, and no benefit I'm aware of.

So the short answer (IMO) is no, but guitar makers use a wide variety of methods to apply shellac to a guitar, and I expect most of them can be made to work.

James
James Lister, luthier, Sheffield UK

ChristianSchwengeler
Luthier
Posts: 1307
Joined: Sun Apr 29, 2012 6:18 pm
Location: Lisbon Portugal

Re: French polishing

Post by ChristianSchwengeler » Mon Apr 08, 2019 1:36 pm

James Lister wrote:
Mon Apr 08, 2019 9:00 am


So the short answer (IMO) is no, but guitar makers use a wide variety of methods to apply shellac to a guitar, and I expect most of them can be made to work.

James
Absolutly - I think the problem lies in the expression "french polish" - and I have seen a lot of people using a much wetter pad than you would expect. What counts for me is the final result and how it looks over time. Sometimes clients return to me instruments for minor set-up so scratchted up that I wonder why I even did worry about the finish.....And the most perfect "french polish" procedure will not avoid that and it is what it is - shellack is not resistant at all! And I see sometimes some spanish guitars which resists pretty well, because it is a much thicker shellack aplication than what would be expected by the purists. :D

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