French polish is a very safe organic finish with superior tone. The finish is slowly built and can be minutely adjusted and repaired. The finish is not very protective however and will scratch and wear more easily than alternatives.
The finish dries almost immediately but takes weeks to months to cure.
Step 1: Vocab
"lac button" or "flake"- a piece of shellac resin.
"cut"- ratio of shellac to solvent in solution.
"application pad/cotton pad/polishing pad/mouse/rubber/tampon/muñeca/polishing pad"- pad used to apply shellac.
"charge"- adding shellac to a pad.
"to pad"- to apply shellac.
"polishing session" - padding session.
"spiriting off"- padding with alcohol to remove excess oil.
Step 2: Materials
small dispense bottles
Step 3: Sanding
Prepare the wood by sanding.
Use 120-400 grits before finishing.
Use 600-1500 grits to level cured shellac between padding sessions.
Use 800 and 1000 grit for building and polishing stages.
Wet sanding: Make a sanding pad from a 2 inch square piece of Styrofoam. Add a few drops of lubricating fluid, like mineral spirits, to the surface and smear around. Add a few drops of oil to lubricate and sand very lightly for only minor flaws. Wipe surface clean with a paper towel.
Step 4: Shellac Flakes
Shellac is a natural material derived from a resin secreted by the lac bug found in South Asia. It is a complex mixture of esters and polyesters of polyhydroxy acids whose composition is highly variable depending on the origin and type of refining. It is sold in flakes to be dissolved in a solvent. You can find flakes from blonde to garnet imparting tones from light golden to orange and amber.
Shellac is naturally waxy and can be purchased with or without the wax removed. Dewaxed varieties are said to have superior clarity and contain less than 1% wax compared to 3-5% in waxy flakes. Dewaxed shellac is also necessary if another finish is to be used over it. many other finishes will not bind to waxy shellac.
To dewax waxy flakes, dissolve in a solvent and wait until the wax settles out and then pour off the top layer into a separate container.
Flakes should be stored in a cool dry place and will last years. Refrigeration will also increase shelf life.
After dewaxed flakes are dissolved in a solvent the shelf life is about 6 months.
For shaded finishes use darker shellacs for some of the building cotes and finish with pale blonde.
Step 5: Solvent
Shellac is water insoluble, but is soluble in ethanol, methanol, isopropyl alcohol and a variety of other substances. Ethyl alcohol (everclear) is preferred over denatured alcohol or methanol as a solvent because the latter is a neurotoxin.
The alcohol smooths and glosses the surface and draws lubricating oil out. Too much alcohol, however, will wipe the shellac finish off the surface.
Keep alcohol in a small dispense bottle to thin shellac in the pad as needed.
Step 6: Shellac Solution
Keep shellac solution in a small squeeze bottle. Freshly made shellac is best. The amount of shellac flake to solvent used is called 'cut'.
1 pound cut shellac = 1lb shellac flake dissolved in 1 gallon alcohol. (1oz flakes to 8oz/1cup alcohol)
2 pound cut = 2lbs shellac flake dissolved in 1 gallon alcohol. (2oz flakes to 8oz/1cup alcohol)
Dissolve the flakes in glass or plastic. It may take 24-48 hours to completely dissolve. Crushing or grinding the flakes will quicken the process. Shake or stir periodically. When dissolved decant through a coffee filter to remove wax and impurities.
Some polishers add gums and resins to the shellac varnish recipe to enhance or improve particular characteristics.
Step 7: Application Pad
An application pad has two parts. An internal wadding and an outer cover cloth.
Internal wadding maintains the application pads shape and firmness. It also absorbs and holds shellac, alcohol, and oil. Common materials include 100% lambs wool, cotton cheese cloth or gauze. The size and shape can be adjusted for the size and shape of the piece being polished. Smaller pads are used for tighter corners. Typically the size is 1-2 inches like a compressed golf ball.
Cover cloth is typically linen or tight weave cotton material. Old high quality sheets, pillow cases or t-shirts can be used. Cut the cloth to 8 inch squares.
An application pad can be made by wrapping a small wad in a cover cloth. Grip the loose end of the cover cloth in the palm and flatten out by pressing it into the palm of the opposite hand. The pad should be a semi-firm flat ball.
While polishing if the pad is too wet, the vapor trail will be so long you cant see the end. If the pad is too dry, there wont be a vapor trail, just a smear of oil on the surface. The vapor trail will shorten with use to just a few inches. This tells you its time to replenish the pad.
An application pad in use can be stored in an airtight container for later use.
Step 8: Oil
Oil is used to lubricate the pad and allow for smooth application of shellac. Common oils include olive oil, paraffin oil, mineral oil (baby oil).
Add a drop of oil periodically to the pad to lubricate over the surface of the shellac layer. Every 2-5 minutes as the pad begins to stick add another drop to the pad. Be conservative with oil. Excess oil can be trapped in the finish and make it cloudy.
Step 9: Pumice
Pumice is an optional addition to the polishing process. It fills and levels the surface of the wood. Ultra fine pumice powder also acts as a mild abrasive, diminishing surface flaws.
To fill pores in porous wood sprinkle some pumice on the surface and rub with a pad that is mostly or all alcohol.
Pumice can also be used to repair damaged areas. Sprinkle a small amount over the damaged area and continue padding shellac. Adjust the amount of pumice for the amount of leveling needed.
A pumice pounce bag can also be used for the application process.
Step 10: Basics of a Padding Session
Remember, it is best to start with small amounts. Too little shellac and alcohol added to the pad have no negative effect, but too much can be disastrous.
Charge the pad by adding of shellac to the pad. Add a drop of oil.
Tamp or press the pad into the palm of opposite hand. Flatten and distribute the liquids.
With light pressure, in a continuous circular motion, rub over the wood surface. Start the circular motion before making contact with the surface. Don't slow down or stop to prevent sticking or damage.
As the pad dries out increase pressure to push out more shellac. When most the shellac is dispensed charge again and add a drop of oil.
Concentrate on small areas and gradually build shellac in the entire area. Use smaller and larger circles as needed. Continue until the whole surface has an even layer of shellac. When each working surface is polished (top, sides, etc), work the surface as a whole.
Spirit off the oil by adding a few drops of alcohol to the pad and polishing the surface in large circles. This should remove excess surface oil.
Charge the pad and add a drop of oil. Continue in this fashion focusing on thin and uneven areas.
When the surface is even and complete add a few drops of alcohol to the pad and aggressively polish the entire surface. Add drops of alcohol as the pad dries. Use a circular motion, then finish with long straight strokes with the grain. This diminishes surface imperfections like swirl marks left by the pad.
The 'session' is complete.
Step 11: Prep Wood
Prepare the wood by sanding all surfaces with 120-220 grit paper. Wipe the surface with naptha or lighter fluid to enhance small scratches. Sand with 320 grit paper. The surface can be wiped with a damp cloth to raise the grain and then sanded again with 320 grit.
Step 12: Initial Sealer Coat
The initial sealer coat seals the entire piece with a wash coat of shellac. This acts as a barrier coat making pore filling easier and preventing pore filler from staining the surface of the wood.
Make a 1 pound cut of shellac. This can be made quickly by diluting out a previously made 2 pound cut.
Pad or brush the entire surface. Apply in one direction with minimal overlapping of strokes.
Let dry at least 1 hour.
Sand very lightly with 320 grit paper.
Step 13: Fill Pores
If polishing porous hardwood fill the pores. This is the most important step if you want a glass smooth finish.
Whether using a pumice or pore filler this step is done after the initial sealer coat.
Pumice can be used to fill pores in hardwoods. Sprinkle pumice on the wood and pad aggressively into pores with alcohol and very little shellac. Filling with pumice can be time and labor intensive.
An alternative to pumice is pore filler. The correct color filler must be selected to best match the wood. Oil and water based fillers are applied differently. With water based filler, thin the paste a little with water, then fill pores and scrape away excess. Let dry for 1 hour and sand with 220 grit paper. Don't worry about sanding off the shellac. Seal the wood and pores again with shellac. Dry for 1 hour. Repeat the whole pore filling process and thin the paste a little more. Dry 1 hour and sand with 220 grit paper. Seal again with shellac.
Step 14: Steps to French Polish
Follow the steps in the basics of a padding session for each of the following sessions using a 2lbs cut of shellac.
First session: Only a very thin layer is formed. Cure at least 2 days.
Second session: Do not sand before. Pad directly over the first cured layer. Recharge the pad often. Do not be concerned with flaws or swirls in the finish. Spirit off the entire surface. Cure for 2 days. Wet sand with 600 grit paper.
Third session: Fill open pores and build up thin areas. Lightly spirit off excess oil. Allow 2 days to cure. Wet sand lightly with 600 grit paper.
Forth session: Continue to build the shellac. Cure for 2 days. Wet sanding with 600 grit paper is optional.
Fifth session: The final building stage. Built to perceptible depth and thickness. Cure for 3 days. It is now hard enough for slightly more aggressive wet sanding with 600 grit paper. Finish with 1200 grit paper wet sanding.
Final session: Use a new cover cloth on the pad. Charge with shellac and a few drops of alcohol. This thinner shellac solution builds more slowly. Diminish fine scratches left from sanding. Stop after the entire surface has a thin smooth coating. Now polish the entire surface with only alcohol added to the pad. Apply a few drops of alcohol to the pad as needed and polish vigorously over the entire surface.
If any flaws remain, let dry for a day and wet sand with 1200 grit paper and polish again with a thinner shellac solution.
Spirit off: Final finish. Cure for 2 days. Oil will still be coming to the surface leaving a lightly cloudy surface. Perform one or two sessions with only alcohol on the pad. Charge a polishing pad with a few drops of alcohol and polish the surface. Use a circular motion and finish with long straight strokes with the grain. Let the piece sit for a day and spirit again if needed.
Polish: If a finer finish is desired a rottenstone and oil solution may be used. The piece must be thoroughly cured before polishing. This will take about 7 days. Use a 2 inch square felt piece as a polishing pad. Add a few drops of oil to the finish, sprinkle with rottenstone and lightly mix. There should be more oil than powder forming a liquid thin paste. Polish the surface in a circular motion. Add oil and powder as necessary. Finish with straight strokes.
The complete process takes 15-20 days plus the final curing time before handling. Some schools of french polishing complete in less than a week, while some take months for a perfect finish.