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Friction Polishing question

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Forum topic by greatview posted 02-03-2018 01:23 PM 474 views 0 times favorited 8 replies Add to Favorites Watch
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greatview

132 posts in 3274 days


02-03-2018 01:23 PM

Topic tags/keywords: question lathe finishing

I’ve been experimenting with friction polishing (1/3 shellac, 1/3 BLO, and 1/3 denatured alcohol) and I’ve gotten excellent results. But, I don’t understand how it works. Shellac hardens when the solvent evaporates. BLO cures by reacting with oxygen which may take a day or more. Shellac can be softened with the application of denatured alcohol. Cured BLO needs a really strong solvent to attack it.

When I apply the mix to a rotating object with a paper towel, the finish appears fully cured and hard within a few minutes. I don’t understand what happens to the BLO. Even with the heat of friction I wouldn’t expect it to cure in a few minutes. But, it appears to be fully cured.

(BLO – boiled linseed oil)

-- Tom, New London, NH


8 replies so far

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johnstoneb

2999 posts in 2289 days


#1 posted 02-03-2018 02:02 PM

I think the friction generates heat and this speeds up the BLO curing reaction. The alcohol thinning the whole solution probably helps also.

-- Bruce, Boise, ID

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John Smith

1308 posts in 279 days


#2 posted 02-03-2018 03:21 PM

Tom, if you google “French Polishing” – you will find some very interesting reading.
I have only used French Polishing a few times and I don’t know the “hows or whys”.
different woods and desired finishes require a different “recipe” of the mixture ingredients.
the Old Masters have used it for centuries. if it works for them, it should work for us.
when you say you apply the mixture to “a rotating object”, I am assuming you are talking
about objects turned on a lathe ?? what wood are you using ? I have applied varnish recipes
and other mixtures to certain hardwoods and they are still “sticky” 2 days later.
your recipe sounds like a better approach than mine to achieve a quick drying finish.

the last time I used it was on a mahogany cabinet that held 8-Track music cassettes,
5 and 7” Reel-to-Reel sound tapes and VHS/Beta VCR tapes. so, that will give you an idea of the time frame.

I don’t think I would like the motorized “friction polishing” unless I was in a high volume furniture shop.
I just like the “hands on craftsmanship” that hand applied polishing techniques give you.

.

-- some people are like a Slinky - - - pretty much good for nothing. But still make you smile when you push them down a flight of stairs.

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Woodknack

12331 posts in 2497 days


#3 posted 02-03-2018 05:16 PM

Some of the blo soaks into the wood and is covered by the shellac which doesn’t care about oil. And some blo ends up in your paper towel. John is right, it’s basically French polishing on a lathe.

-- Rick M, http://thewoodknack.blogspot.com/

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johnstoneb

2999 posts in 2289 days


#4 posted 02-03-2018 05:34 PM

There is a big difference between friction polish and French polish. Friction polish uses the heat generated during application to cure the finish.
http://azwoodturners.org/pages/tips/HomemadeFrictionPolish.pdf

French polish is a two stage finish. First stage uses a pad with shellac, light oil (such as walnut oil) and pumice applied by hand with a small pad. The pumice is an abrasive that cut the wood lightly and fills the pores in the wood the shellac dries and keeps the pores filled. A second pad is used after the pore filling is complete with shellac and some oil as a lubricant. The shellac is rubbed onto the surface many times. This is a time consuming finish as you put many light coats of shellac on building the finish.

-- Bruce, Boise, ID

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John Smith

1308 posts in 279 days


#5 posted 02-03-2018 05:53 PM

wow – THANKS BRUCE !! very interesting article.
I printed it out to go with my other “how to” collections.

one quick question (to anyone) – - – how do you think the French/Friction polish will stand up over time
under normal use compared to several coats of a good varnish or polyurethane on tool handles
such as chisels, hammers, gouges, mallets, etc. ??
it seems as though the sweat and salt from the bare hands would somehow affect the shellac ?

-- some people are like a Slinky - - - pretty much good for nothing. But still make you smile when you push them down a flight of stairs.

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johnstoneb

2999 posts in 2289 days


#6 posted 02-03-2018 06:41 PM

I don’t think there would be much difference. The poly might hold up a little better just because it is a more modern finish. I like shellac it won’t hold up to alcohol because that is its solvent. The friction polish because BLO is part of the finish would give you that oil penetration. A French polish finish is pretty much straight shellac. The oil is just used to lube the pad you only use a drop or to at a time. Shellac has been used for many years and has held up well.
For my tool handles I generally just use BLO It holds up well and easy to apply if it starts showing wear.

-- Bruce, Boise, ID

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Woodknack

12331 posts in 2497 days


#7 posted 02-03-2018 07:46 PM


one quick question (to anyone) – - – how do you think the French/Friction polish will stand up over time
under normal use compared to several coats of a good varnish or polyurethane on tool handles

- John Smith

I used it for a few years and found it to be fine for things that you don’t touch, but you’ll lose the gloss quickly by handling. Even if you don’t handle it, the gloss will fade. If you don’t care about gloss, it’s fine. I don’t use it anymore. I now use straight shellac or waterbase finishes, and buff it. I find it to be more durable.

-- Rick M, http://thewoodknack.blogspot.com/

View Aj2's profile

Aj2

1656 posts in 1915 days


#8 posted 02-03-2018 10:11 PM

I just call it polish. Shellac is my favorite finish I don’t really like adding oils anymore but I used to use mineral oil, olive oil. But I’ve found once I get a good build denatured will quickly level out shellac or polish . The best shellac finish is hardly noticeable.

-- Aj

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