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I was laying down shellac tonight, testing some newly arrived batches of flakes for drying. I didn't use oil, just so that variable would be out of the picture. I got a decent build, though with more effort from the friction. The mix was less than 1 lb, probably close to 1/2, so it was slow. Aside from the extra effort, would the lack of oil cause any other problems?

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now known around here as Pat Foster
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http://www.patfosterguitars.com

As far as I'm aware the oil is purely a lubricant. There are a few people who don't use any oil at all when padding shellac. See GAL Big Red Book Two for a discussion on French Polishing with Cyndy Burton, Greg Byers, Robert Stenegger and Buzz Vineyard. Cyndy doesn't use any oil during body sessions and she mentions having had problems with oil trapped under the finish.

MichaelP is the FP guru and will no doubt chime in with his sagely advise on the matter.

Cheers Martin

Pat,
Oil is just a lubricant. 1/2# cut is a very light cut. Probably the reason you were able to body with out oil. I have to say though I recommend a 1# cut for sealing and glazing and 2# for boding

Martin,
In regards to oil trapped under finish . The only way virgin Olive oil or Walnut oil gets trapped under finish is if a continuous film is applied with allowing the the oil to rise to the surface after each boding session and failing to spirit off. No knock on Cindy but the wrong type oil will cause this or as I mentioned before piling body session after body session with out spiriting off.

Ditto what Michael said. I would also be worried that in order to polish without oil, you will need to press a little harder and move faster than required to avoid "sticky" marks, and you might end up removing more shellac than you add, especially if you are only using a 1/2# cut.

John

What is the difference between, olive oil or walnut oil and, say, mineral oil, grape seed oil, or peanut oil, if they are spirited off after bodying sessions?

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Waddy

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Sound Clips of most of my guitars

They may all be fine as long as ther are no additives. Extra Virgn Olive oil and Walnut oil are a good viscosity for the job and are the trditional oils used. Grape seed and peanut oil I have no experiance with.

The oil (I use walnut as it's a drying oil) allows you to apply just that little extra pressure when working which I believe creates a harder finish and will also lead to a smoother better glazed one. I never use any form of abrasive on my finish once I start to FP and the oil allows a smoother glide for the muneca leaving less ridging on the finish. I allow 2-4 hours between bodying sessions (two a day) which gives plenty of time for the oil to come to the surface before spiriting off.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Great info. Thanks, all!

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now known around here as Pat Foster
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http://www.patfosterguitars.com

Pat...what Michael and John E. say.

I've FP'd 4 guitars now and mostly used 1# and 2# as Michael describes. I try to use as little oil as possible but you need some. Once you feel the pad dragging with the highest force on the pad you can muster, it's time for oil. I never use more than a TINY drop spread out on the pad. I've found that less is much better...and it goes a long way. Try to avoid those sticking marks like the plague!

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JJ
Napa, CA
http://www.DonohueGuitars.com

Collin,
Great minds tend to French polish and not sand We keep trying to tell them, "There is no need to level sand if you do the process and not short cut it"

Waddy asked:
"What is the difference between, olive oil or walnut oil and, say, mineral oil, grape seed oil, or peanut oil, if they are spirited off after bodying sessions? "

You can think of oils as faling into two classes, although they shade off in the middle, of course. Mineral oils are basically non-drying, while many of the vegetable oils are drying oils.

There is a test, yielding an 'iodine number', which predicts how fast an oil will dry in air. Tung oil and linseed oils have high iodine numbers, IIRC, and dry quickly, while mineral oil and olive oil have low iodine numbers. A friend of mine told of somebody he knew who made some oil varnish with olive oil, and all it did was turn rancid on his guitar without drying. Other drying oils are walnut oil (which was used by early oil painters in southern Europe, where they don't grow flax), safflower oil, poppy oil, and so on. Another non-drying oil is 'parrafin oil', also called 'Rubcut oil', which is a fraction of mineral oil that is heavier than kerosene and lighter than mineral oil.

You can easily see for yourself whether you are using a drying oil by doing a 'draw down' test. Get a nice clean piece of glass and a single edge razor blade. Put a piece of tape over the edge of the blade on either end, leaving a half inch or so uncovered. Put a drop of oil on the glass, and use the razor as a squeegee to draw the drop into a film of uniform thickness. Label the piece and set it aside. Check it every once in a while to see if the oil shows signs of drying. This is a standard test that I learned about from the late Mort Hutchins, Carleen's husband, who worked as a color chemist for Hercules plastics.

BTW, if you're using walnut oil, and need it to harden, it's a good idea to do a draw down. Many of us get raw, cold pressed walnut oil from health food stores. It turns out that they use the same presses for making all sorts of oils, and even a little rapeseed (canola) oil in a batch of walnut can destroy it's drying qualities. If the batch you got won't harden, use it on salad and get another bottle.

Drying oil seems to combine chemically with the shellac, or, at least, with the seedlac I use. The resulting film is a bit less soluble in alcohol, and a little tougher. It also gets from the oil a tendancy to darken with age, and to shrink and craze.

Because of this I have gone to using as little oil as I can get away with. Practically speaking, I only use oil in the final French polishing, after all of the build is done. I do use Micromesh, smoothing off the dust particles at the start of each bodying session, so I guess I'm not a 'purist'. Once you get the hang of it, it's not too hard to get an even build with no oil.

I started this exercise to compare the shellac flakes from Woodcraft and LMI after a recent thread here mentioned how some shellac flakes didn't dissolve completely. Flakes from both sources were bought in the last two months. The flakes from LMI definitely dissolved more quickly and more completely, in the case of both the light and darker types. The shellac from the LMI flakes cured more quickly. The finish from the LMI flakes "seems" harder, though I have no way of quantifying this. I left out the oil in this comparison to eliminate a variable and found that I was getting a decent build without it.

I plan to draw down the walnut oil I have as Alan suggested, and from the other things I've learned from this thread, will put off using oil until the last session.

Thanks again for all the great input!

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now known around here as Pat Foster
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http://www.patfosterguitars.com

[QUOTE=MichaelP] Collin,
Great minds tend to French polish and not sand We keep trying to tell them, "There is no need to level sand if you do the process and not short cut it"[/QUOTE]

Michael, I know, but if we keep on at them often enough eventually it'll sink in (or should that be rub off?)

Each session has the ability to level the one before, until when you glaze, you end up with a super smooth surface. Using the oil makes this levelling much easier.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

I buy walnut oil from Mike Mahony a well known woodturner ( my other passion) he sells it for a finish on salad bowls and utility bowls.His oil drys clear and hard,It is a great finish for bowls that get used for every day use Its works great for FP.If you yahoo his name it is the second or third name that comes up.He also sells walnut paste wax that I've used for other turnings.