FINISHING SECRETS . . .|
9. Shellac and a "French" Polish
Thus far, this series has described the use of oils and varnishes for a finish that can be best described as a "soft gloss". But, these finishes can leave something to be desired when we have a piece of wood with a highly figured or a complex grain pattern that is best displayed with a deep high gloss finish. We could achieve this high gloss surface with multiple coats of varnish that is then sanded and polished, but it will never be as brilliant or have the depth of a French polish (shellac) or high gloss lacquer.
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Shellac is an excellent finish, but one that is normally thought as easily damaged by water, alcohol, and food acids. This reputation is not deserved because pure shellac is nearly waterproof, and damaged only by very strong alcohol and acids. To prove this, drop a shellac flake in a container of water and it will not dissolve. Put it in your mouth, and the acid in your saliva will dissolve it.
Shellac is totally "food safe" and it is used in many prepared foods, and as a coating for candies and medicines.
The traditional French Polish uses pumice fillers, shellac, and oil that are applied with a wool ball wrapped in linen. The techniques are complex, time consuming, and hard work. However, we can take advantage of modern materials and the lathe. While the total effort is much less, this method of application is most suitable for pieces that are turned-all-over and that can be finished on the lathe. We could adapt these same techniques for "off the lathe" with muscle power replacing the horsepower. However, for "natural edged" and other pieces with unfinished areas, I prefer to use the gloss lacquer finish described in Article 11 of this series.
The French Polish, as described here, is one of those techniques where a 15-minute demonstration takes the place of an entire book. I will attempt to explain it in a few paragraphs.
The commercial pre-mixed shellacs contain preservatives, water, and wax to extend their shelf life while making the shellac less desirable and durable for finishing. However, dry shellac flakes have an infinite (Refer Addendum) shelf life, and by mixing your own, it is always fresh. I use "Super-Blonde" or "extra pale" flakes because of their light color. I fill a graduated pint Mason jar to ¼ with flakes, then fill to just a bit over 1/2 full with denatured alcohol. This is roughly the equivalent of what the trade calls a 2-pound cut, or 2-pounds of shellac flakes in one gallon of denatured alcohol. I de-wax all shellac by letting the mixture set for several days until any wax settles out as a cloudy layer in the bottom of the jar, then decant the clear liquid into a clean jar and throw away the remainder. I treat all shellac flakes the same because they often contain a small amount of wax residue, even though they may be labeled as "dewaxed". This is particularly true of less expensive flakes.
The shellac will have a shelf life of 2 to 3 months after it is mixed, so I always date the container after mixing, and test before using. The test is simple - place a drop on the surface of a piece of glass, and wait overnight. If it is brittle and pops off of the surface, it is OK to use. If it is rubbery, throw it away. There is no way to resurrect old shellac, so don't even try.
Use a small piece of new terry velour toweling as an applicator. The velour will form a smooth uniform glaze on its surface, eliminating surface lines caused by the fabric texture. It doesn't have to be white, but it has to be new. A washed towel will have a residual detergent deposit that will interfere with the finish, and the clothes dryer will harden the ends of the cotton fibers.
For bowls, I make a ball from either a piece of cheesecloth or a single sheet of VivaÒ paper towel, and wrap it in a square of the velour toweling. For spindle turnings, I cut strips about 1" wide and 6" long, and fold them in half with the velour side out, making a double-sided applicator.
The ball can be reused by storing it in a closed container with about ¼" of denatured alcohol in the bottom. This prevents having to break-in a new one every time you apply the finish.
The wood surface must be as close to perfect as you can get it. The high gloss will accent every hole, rough spot, scratch, or tool mark. Deep scratches can be telegraphed to the surface and magnified. Sand in both directions to at least 600-grit, and 1500 or 2000 is even better. Dampen the surface to raise the grain, and lightly sand again starting at 600-grit.
Hard and closed grain woods like Maple need no other preparation then sanding. Porous or open grain will benefit from a sealer. Pumice was traditionally applied with oil for a grain filler and sealer, but that was before CA glues were invented. Apply the CA glue, and then sand away or all of the surface film because we are using it as a sealer, not as a finish. I apply an even coat of thin CA with a wad of synthetic batting stuck to a piece of masking tape to keep it off of my fingers. The cellulose in paper towels and cotton products acts as an accelerator.
The oil is used as a lubricant between the applicator and the surface. There is an ancient controversy over whether any oil remaining on the surface should or shouldn't become a part of the finish. Many French Polish techniques use drying oils such as boiled linseed, walnut, tung, etc., and some finishers may even add them to the shellac, For my own finishing, I have never been able to decide between mineral oil, which doesn't, or linseed oil, which does. So, I use both. Which one depends on my mood at the time. Sometimes I give up and use Mystery Oil just to prove to myself that it really doesn't matter. I think that I have had better results with mineral oil that was thinned with a little kerosene.
Decant the shellac and oil into small squeeze bottles. These are handier than trying to pour small quantities from a can or jar.
Put a small amount, about ½ teaspoon, of shellac on the applicator pad or strip. Surround the shellac on the pad with a ring of a similar quantity of oil. If using the strip, fold it in half and place the oil next to the shellac.
Running the lathe at a moderate speed, hold the applicator pad so that the shellac is applied to the surface with the oil following immediately behind it. It will get hot. If it tries to grab the applicator pad away from you, add a little more shellac and oil. If it doesn't get hot, there is too much oil on the surface and it needs to be removed with some soft toilet tissue. Add more oil and shellac only if necessary, less is better. Then, go back in the opposite direction with the oil part of the applicator again trailing the shellac. Repeat no more than five (5) times, adding shellac and oil as required. The new surface will be quite soft, and it will start to drag if too many coats are applied.
A second application of five (5) coats of shellac will "deepen" the finish and improve its gloss. Let the shellac dry overnight before making another application. Remove any excess surface oil with a clean velour pad or soft toilet tissue, and buff the surface with 0000-steel wool.
Once mastered, it is a relatively easy finish to apply. But, it will take a lot of practice to get the right combination of lathe speed, amounts of shellac and oil, and application technique. The reward will be a higher gloss than you ever thought possible.
The Final Touch
We should wait at least a week, preferably two, before handling the finished piece. The shellac is very soft immediately after it has been applied, and is easily damaged or abraded from handling. Shellac will continue to dry and harden for several years, depending on the environment, but a couple weeks is usually sufficient for normal handling and polishing.
The surface gloss can be improved after the finish has sat for a couple days. Add a small amount of straight denatured alcohol to a new applicator pad, and lightly whisk it across the surface. DO NOT RUB because this will soften the shellac and damage the gloss.
If you can't live with any circular ridges that may remain in the surface finish, they can be removed with 0000-steel wool that is rubbed across the ridges after the piece has set for at least two weeks. To restore the gloss, polish the surface with 4F pumice, followed by Rottenstone, using the velour cloth as an applicator and raw linseed oil or mineral oil as a lubricant.
The shellac can also be buffed with White Diamond compound on a linen wheel to achieve a spectacular gloss. However, the buffing is harder on the surface than hand polishing and the shellac must be very hard. I get the best results from buffing when the piece has had at least three months for the finish to cure before buffing, and a year is even better. This is definitely not a "quick" finish, but it is definitely worth the wait.
Apply a coating of paste wax for protection of the surface. Beeswax, TrewaxÒ or Minwax® finishing waxes are good for this purpose. Do not use a stick wax because the heat required to melt the wax will damage the shellac surface.
© 2002 - 2009 by Russ Fairfield. All rights reserved.
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