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Brad Sears - French Polishing - March 2013

Brad Sears Fine Woodturning

6213 Blackberry Terrace
East Stroudsburg, PA 18301
www.turningarts.com
(570) 807-8100
brad@turningarts.com

French Polishing on the Wood Lathe

By Brad Sears

Author’s note: The following is excerpted from a blog post 1 I wrote in December, 2010 elaborating on the French Polishing process published earlier in the year.

Back in June 2010, I published what has become a very popular post about French Polishing. Since then, I've gotten several requests for more information. So here goes...

First, surface preparation is key. Any finish is only as good as the surface to which it’s applied. So the surface should be clean, dry and sanded to at least 600-grit. And secondly, the materials…

Shellac. I use a hand-mixed shellac using a garnet button lac called "bysakhi" that I buy from Shellac.net mixed to a 2 lb cut. I mix and store about a 2-week supply in a plastic squeeze bottle. We want our shellac very fresh!

I grind the shellac "buttons" in a cheap electric blade coffee grinder and dissolve the resulting powder in 190-proof grain alcohol, available in liquor stores in most states (PA requires a license easily obtained from the state Liquor Control Board) I do avoid commercial denatured alcohol (DNA), because (a) it's anything BUT eco-friendly and
(b) don't think it works as well as grain alcohol.

Alcohol. You'll also need another squeeze bottle containing nothing but pure grain alcohol for diluting the shellac in Step 3 of the french-polishing process.

Oil. I use pure (it's actually "kosher") walnut oil that I buy in bulk from JEdwards (http://www.bulknaturaloils.com/Category/651-bulk-walnut-oil.aspx) in Cambridge, MA. Any vegetable oil will work, but I like walnut oil because I think it gives a slightly harder finish, it's inexpensive and I keep a lot on hand for finishing my wood turned bowls. (BTW, for the bowl turners in the audience, walnut is a penetrating oil that hardens (polymerizes) to form a durable finish that's food-safe right from the get-go. No waiting 72 - or more - hours to "cure.")

Pumice. We use 4F pumice, available from most hardware stores, in the pore filling process.

Cloth. I use either a section of new, pure cotton velour toweling or sections of an old cotton undershirt folded into 3 - 4 layers, which I hold against the workpiece with my index finger. (That said: please use common sense and be very careful about wrapping cloth around your finger - and don't get anything caught in the lathe. Accidents can happen in a millisecond if you're not paying attention! Safety first....)

Ok, so let's get to it. There are three basic steps to French Polishing on the wood lathe:

1. The first is provide a base layer of shellac (also called “bodying-up”) that will be used in the wood pore filling step (step 2.) We do this by applying multiple heavy layers of shellac while running the lathe at VERY low speed. We wet our folded rag with a dozen or more drops of shellac and apply the shellac to the workpiece using finger
pressure.

Let me say this again: slow speed is critical to your success. Our hand-mixed shellac dries very quickly and will streak very badly if you apply it at too high rate of speed. As an example, I finish my pepper mills (~3" in diameter) at about 120 rpm. Larger pieces are turned even slower. A 14" platter might be turned at 20 - 40 rpm. Use the hand wheel if your lathe can't be turned-down that low. Apply a drop of oil to the rag and spread it around with a finger if you find the rag dragging or sticking to the workpiece.

After applying 2 - 3 passes of shellac, we speed the lathe up to 500 - 600 rpm, let it run for a few seconds, then buff the workpiece using a DRY section of rag. There are two objectives here: (1) although the alcohol will have mostly evaporated, we need to force out any adulterants (mainly water) that might remain in the finish and (2) to level out
the previously applied shellac. The finish will "cloud" as we start, due to mild abrasion from the cloth. Our shellac is still very soft at this point, so start with minimal pressure and gradually increase pressure as the finish clears. Change sections of the cloth periodically until the cloth comes away clean. This only takes a minute or so.

Repeat the process until the pores are covered. Close grained maples may only take one repetition, while open-grained woods like ash or hickory might take 4 - 5 passes.  It's tough to over-do at this stage, so I find a little more is generally better. We can also add a drop of oil to the rag along with the shellac if the rag drags or pulls on the workpiece.

2. Step 2: Pore filling. Shake a small amount of pumice (or rottenstone) onto a sheet of paper. Spread it around to an even thickness - about 1/16th of an inch works for me.Now, we wet our rag with 4 - 5 drops of shellac, apply a drop of oil and mix the two together with a finger. Backing the wet section of rag with our finger, we dab a "cut" of pumice onto the wet rag from the paper. Next (and this is important!) spread the pumice around the wet portion of the rag with another finger until the pumice "clarifies." (We REALLY don't want to apply unclarified pumice/rotten-stone to the
turning workpiece.)

Now press the shellac/oil/pumice into the turning workpiece while moving your finger in a circular or "figure-8" motion. Work on about an inch or two at a time until the entire workpiece is covered. The finish again will "cloud". Stop and re-load your rag when the finish starts to clarify. We can get a little aggressive here and apply some pressure with our finger into the workpiece. When you hear a "swishing" sound, you know the process is working.

Repeat until we've made 3 - 4 passes over the entire workpiece. You will see a skim of stuff coming off the trailing edge of the cloth - and often layers of cloth will be worn away. Then you really know the process is working!

What's happening is this: The alcohol in the shellac is dissolving some of the previous coats of shellac while the pumice/rotten-stone is "sanding" down/leveling the microscopic ridges on the wood surface creating loose wood fibers that then combine with the pumice and shellac to create an amalgam that fills the pores in the surface of the workpiece - and is held in place by the shellac. Instant wood filler!

Now, run the lathe up to 500-600 rpm and again buff using a dry section of cloth. We are now removing any loose wood fibers, excess pumice/rotten-stone, forcing out any adulterants, and again leveling our finish. At the end of this step, we should have what would ordinarily pass as a reasonable "friction polish." But the best is yet to come.

Quick note: you can repeat Step 2 as often as you need at any subsequent point in the process if/when you mess-up the finish. Step 2 is also where I often start repairs to a damaged french-polished finish.

For most work, we can go right to Step 3, but if we're looking for the ultimate finish, it's sometimes good idea to let the workpiece sit overnight (or even for 2 -3 days) to let the finish really "gas-out" and harden a bit more before proceeding to the final steps. Experience will guide you.

3. Now the rewarding part: French polishing. Take a clean section of rag, fold it over 2 - 3 times and apply 5 - 6 drops of shellac. Next, take the squeeze bottle of pure alcohol and dilute the shellac by about 50% (the amount isn't critical - just get in the ballpark - we just want very thin shellac at this point) and apply a drop of oil. Use another finger to spread the mixture around. We want everything well-mixed before our wet rag touches the turning workpiece.

Running the lathe at slow speed, gradually work the diluted shellac/oil mixture into the workpiece - once again in a circular/figure-8 motion, using some firm finger pressure. (The idea is to cause the alcohol to partially dissolve the underlying shellac so as to form a firm bond with the next "micro-coat" of shellac and oil. Don't get carried away and try to muscle things, no broken fingers or workpieces here....) Again the finish will "cloud" but soon clears. That tells us the shellac is being applied. Re-load the rag with shellac/alcohol and a drop of oil and repeat the process whenever the "cloud" disappears.

By now, the finish should begin to really shine!

After we've covered the entire workpiece 4 - 5 times, we once again speed the lathe up to 500 - 600 rpm and buff with a dry cloth until the finish takes on a spectacular shine. We repeat Step 3 again, if necessary. (Once we get the technique down, the finish at this point will be amazing! Note: If you want to continue french-polishing beyond 2 - 3 repetitions of Step 3, it's a good idea to let the piece sit overnight to "gas-out" and harden. Again, use your judgment.)

4. Optionally, we can apply a coat of wax. I use either beeswax of carnauba wax to give a layer of protection against spills (Caveat: alcohol - like from a spilled glass of wine - will harm our finish. Remember, we've been using alcohol as a solvent throughout. If this happens, all is not lost. Simply re-mount the piece on the lathe, and re-start at step
2.)

And that's about it. Like any new technique, French-Polishing on the lathe requires a certain amount of practice to get right. But with a little patience....




To give you an idea of time, it typically takes me about a week to French-polish one of my pepper mills. So the process isn't terribly quick, but it beats the 3 - 4 weeks normally required of the manual process.

Copyright © 2011 Brad Sears Fine Woodturning All Rights Reserved (Used with Permission)
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Apr 24, 2013, 7:15 AM