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sequoia
10-22-2015, 05:57 PM
I'm making a new thread here because I think this French polish technique has real merit and could be an option and I wanted to show the results. Oh, and also I wanted to show off my latest uke which turned out rather well I think.

Basically, this was a shellac based finish using alcohol mixed with acetone to make a highly dilute solution of shellac which flashes off in seconds. The solution is applied in a continuous way that lays down extremely thin layers quickly and does not use oil. The build is thin but fast. In theory, a French polish could be done in one day.

The reality was a bit different. Here are my observations. First the good:

- The toxicity was low and the fumes manageable with a fan. No moonsuit and respirator needed like nitro.

- Since the solution was so thin it was hard to screw up with runs, fisheyes, etc. etc. Very forgiving.

- No spray equipment needed

- Cheap: Cost in materials per ukulele about $US 2.00 dollars.

- No oil used so no "spiriting off" steps needed

- Burn in is good because of the high solvent level and adhesion good

- Pleasant and enjoyable to apply in a Zen sort of way without the monotony of a hard core French polish

Now for the drawbacks:

- Lot of flammable fumes in the shop. No sparks. No smoking for sure

- Sticking was an occasional problem. But you just move on and come back later.

- dry times after a session is still an issue. Quicker but as coats build there is still dry time.

- Really darkens the wood (see pictures) as the solvent penetrates deeply. Not necessarily a bad things as it pulls deep grain.

- Final dry time before final level sand and polish is forever just like a traditional French polish. It can be polished "green" but I did the sniff test and it took better than 2 weeks.

So the results. A local California bay laurel top with mahogany and coco binding. Check out the cool 3-d effect on the laurel. Pictures don't do it justice. Oh, and how does it sound? Make yo mama cry it's so sweet.

84571

84572

84573

84574

84575

lauburu
10-23-2015, 08:45 AM
a shellac based finish using alcohol mixed with acetone
What were the ratios of shellac/alcohol/acetone you used


It can be polished "green"
Could you please explain this

Thanks
Miguel

pbagley
10-23-2015, 09:18 AM
Thank you for posting this. Very interesting stuff, even for us amateur builders.

Questions from someone with limited experience:
- Can this be applied over a coat of oil finish. I'm thinking a light oil like lemongrass oil, which I've used to enhance the figure and grain under a urethane finish. Of course there would be the dry time associated with the oil finish before applying the shellac. With the comment of darkening the wood above, would the oil finish be necessary to show the figure?
- Have you seen any unfortunate reactions with materials like rubber or plastics (etc.) using the alcohol/acetone mix? My one and only instrument finished in shellac reacted with the rubber coating on an instrument stand. This reaction seems to have decreased over time.
- I've found shellac to be very fragile initially, better after weeks or months of drying. Does the alcohol/acetone mix harden faster and get tougher?
Thanks!

Quick edit : That is a lovely ukulele. Very nice.

Michael N.
10-23-2015, 09:37 AM
It might harden faster. I doubt it will get any harder or tougher. Acetone is just the solvent, once it's gone . . . it's gone. You are left with Shellac.

weerpool
10-23-2015, 11:33 AM
its hard to see from the dimly lit photos. do the under-the-light technique then we really know

sequoia
10-23-2015, 11:55 AM
What were the ratios of shellac/alcohol/acetone you used


Could you please explain this

Thanks
Miguel

It needs to said here that I am not a professional luthier and your results may vary. Nor am I the originator of this technique. As always: Test on scrap before using on your instrument. I think this technique is probably best suited to the professional luthier who needs to kick out a finished product very fast. Otherwise, what's the hurry?

- I used a ratio of about 1 to 4 alcohol to acetone. The shellac was about a 1 pound cut. Final coats were less dilute.

- "Green" means "tender" or not fully dry.

- Can this be applied over a coat of oil finish. In a word: Not a good idea

- Unfortunate reaction to rubber or plastics? Very much so. Acetone melts plastic

- Harden faster or get tougher? Yes it hardens faster but will have nothing to do with making the finish tougher. Shellac is shellac. That being said, there is product out of Australia called "hard shellac" that has a plasticiser added that claims to make a more durable finish. I don't know. I have no experience with the stuff.

sequoia
10-23-2015, 07:32 PM
its hard to see from the dimly lit photos. do the under-the-light technique then we really know

Thank you Weerpool for your feedback. I'm sorry you didn't like the dimly lit photos. Best I can do. Not sure what the "under-the-light techique" is. Perhaps you could send us some examples of your ukes "under the light" so I would know? Thanks again and look forward to hearing from you.

Allen
10-24-2015, 12:18 AM
Both the alcohol and the acetone in your mix are nothing more than solvents that will evaporate in a relatively short time. By applying them on in a very thin mix, you do achieve a result that might be considered advantageous. Many thin coats are better than few thick ones. Those solvents will gas off quicker if they aren't trapped under an overly thick layer that develops what is considered a "skin".

But the overall hardening of the shellac still takes time.

There is a never ending list of ways to get a spectacular finish faster.....but I've been in the refinish game my entire working life and have never come across the magic bullet that others claim. They all have trade off's in one way or another.

My advice is to come to grips with the fact that unless it's anything more than a few wipes of oil, you will need to spend between 1/4 and 1/3 of the time to build an instrument just on the finish. If you wan't a truly spectacular finish it could be more......and learn to enjoy that time.

pbagley
10-24-2015, 04:18 AM
Thank you for the advice. Finishing has always been my biggest challenge. 1/3 the time on finishing is about right in my very limited experience.

Michael N.
10-24-2015, 09:39 AM
If I spent 1/3 rd the time on finishing I'd give up. I don't see the point of spending so much time on putting a bit of tree sap on a bit of wood.
Mine is more like 1/10 th, perhaps a little less - including pore filling.

sequoia
10-24-2015, 05:53 PM
. I don't see the point of spending so much time on putting a bit of tree sap on a bit of wood.

Actually Michael it is more like putting dissolved bug egg cases on wood which is kind of weird when you think about it. I hear you. But here is the thing: I enjoy the process and results (usually) and finishing is an enjoyable part of the build process for me. Seeing the wood come alive has always fascinated me. I do not enjoy the process of putting nitro cellulose on wood as much as shellac although I do like the results that nitro gives me, but it isn't nearly as much fun. They don't call it "finishing" for nothing. That bug goo does bring out the grain. Before and after:

84635

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gerardg
10-24-2015, 07:10 PM
See here sort of French polish.
Not realy.
Danish Oil finish.
With dry sand paper (# 400 to #2000 grit - Tamiya brand paper).
14 steps (coats), I repeat each step with same grade paper twice, 24 h. drying time between each coat.
On these pics, just in progress: waiting about 7-10 days before polishing with soft coton cloth.
Many pics on my web site,
see archive files too for process pics.

84638
84639

Some videos here :

https://www.youtube.com/watch?v=rjClfJ4UF40

https://www.youtube.com/watch?v=1HKKkvhDN5M

https://www.youtube.com/watch?v=EKqPh4AjqJg

Michael N.
10-25-2015, 12:44 AM
Someone on another forum mentioned a French Polishing DVD in which the presenter mentioned taking 40 hours to finish (i.e. F. Polish) a Guitar. Perhaps the guy misheard him but if true I view that 40 hours as a form of madness. Fine if you are a beginner but ridiculous if you have any kind of experience.
Back in the early 80's I learnt French Polishing from someone who did it for a living. He was an old style French Polisher. Both his father and grandfather had been French polishers, he could trace the family business back to the very early 1900's. He didn't use the more modern approach of using abrasives and polishing compounds to give the final gloss. Only one abrasive was ever used, 800G. That was used only once, to level the surface. 800G will give severe scratches but these were removed with highly dilute shellac, done with the pad in straight lines. The final glaze was done with a touch of oil and a few drops of alcohol, very dry pad. That was it. A fuss free finish. As a guitar finish it would probably be seen as though it had been applied by someone a little unskilled. Far from it, the guy had a lifetime of French Polishing behind him. The difference was that he didn't use the method of going through finer and finer grits, polishing compounds, until the surface took on the appearance of glass. I refer to it as 'polishing the lens'. In reality it's very difficult to tell the difference between an Oil varnish, N. cellulose or French Polishing when using the abrasive technique. It's very difficult to tell because they are all subject to the very same method of obtaining the final finish. With the more traditional approach the cloth leaves micro lines in the finish (NOT swirls). The very slight texture is enough to avoid the extremely hard glass like appearance. In other words it's a little more organic looking but unskilled it certainly isn't. In fact the process requires more skill (but less time) than someone who goes through finer and finer abrasives. Pretty much any beginner can learn to do that in a matter of minutes.
That traditional approach is what I use. I also use a 'hybrid' form of applying shellac, mainly using a brush. Only the very final surface finish is done with a pad. Applying shellac with a brush (Spirit varnishing) cuts my time down from around 8 hours (on a guitar) to less than 5. Visually I can't tell the difference between a fully French Polished surface and one that has been mainly brushed on. French Polishing does guarantee (almost certainly) that the finish is very thin. It's also better at filling any slightly open pores.

Michael N.
10-25-2015, 02:07 AM
Oh and Gerardg's Danish Oil can also be a very quick finish. Most Danish oils contain some sort of resin, so effectively it is an Oil varnish that has been thinned with plenty of solvent. That allows the wipe on coats. Apply enough coats and you can get it very glossy. Polish it and it will look just like any other highly polished glossy finish. It just takes many, many coats but each coat only takes a few minutes to apply. That's assuming gloss is what you are after. Some just use a few wipe on wipe off coats, which gives a slight sheen. Nothing wrong with it as a finish but it's not quite as protective, very easy to renew though.

erich@muttcrew.net
10-27-2015, 07:06 AM
I also use a 'hybrid' form of applying shellac, mainly using a brush. Only the very final surface finish is done with a pad.

What mix of shellac:alcohol do you use for the brush-on? I've tried it with the standard mix that I use for FP, but found that it left streaks and also tended to drip over the edges, so I gave up on the brush and have just done FP with a pad.

Michael N.
10-28-2015, 01:41 AM
It's very thin, watery thin. Perhaps a 1 lb cut or even thinner. You might think of adding a retarder. I use a few drops of spike oil of lavender. Dewaxed shellac is harder to brush than shellac with the wax left in.
It requires many coats for a full gloss finish, perhaps as many as 20 but each coat only takes a few minutes to put on. Get them all on over a period of no more than 3 days. Then let it all harden for 10 to 14 days. You have to wipe the adjacent edge with your finger to remove any build up of shellac. Use slightly overlapping coats, going across the back or the top. Obviously you can't brush it out like you can with a slow drying oil varnish. If you miss an area don't try to fix it, just leave it. You'll probably cover it on the next coat. Small ridges/brush marks are OK. Big ridges/marks are difficult to recover from. Ultimately it takes practice, don't expect to get good results until you've put some hours in. You can always practice on scrap wood. Use a soft brush. I use a Hake hair brush that is normally used for watercolour painting. You can get a set of 3 for not much more than 5. I have single brushes that cost 30 but I prefer the Hake brush.
After it's all hardened I level with 800G (wet). Then I use the pad in straight lines - just very short quick sessions done many times until all the scratches are gone. That's probably with a 1/2 lb cut. You can use Oil if you want to.