What French Polishing Really Is

Strip away the mystique and French polishing is a simple proposition: shellac resin dissolved in spirit, worked into a surface in dozens of whisper-thin layers until it glows. The resin is harvested from the lac beetle, sold as flakes or buttons, and cut with methylated spirits to make a working solution. The applicator is a pad — traditionally called a rubber or a fad — made from cotton wadding wrapped in a tight, smooth cloth.

The magic is in how the finish behaves. Because shellac is dissolved rather than cured by a chemical reaction, each fresh pass softens the layer beneath and fuses with it. What you end up with is not a stack of coatings but one continuous amber film, perhaps a tenth of a millimetre thick, sitting on the timber rather than buried in it.

Why Shellac Suits Period Furniture

Mahogany, walnut and oak were polished this way for two centuries, and there are good practical reasons to keep doing it.

• Repairable: a scratch, a ring mark or a dull patch can be re-amalgamated with a little spirit and fresh shellac. The new work dissolves into the old and the join disappears.
• Reversible: a restorer in fifty years' time can lift the whole finish with spirit and start again without touching the wood. Conservation ethics depend on this.
• Depth: thin films let light pass into the grain before bouncing back, which is what gives figured mahogany its shifting, three-dimensional quality.
• Control of colour: garnet and button shellac add warmth to dark mahogany, orange shellac sits well on walnut, and pale de-waxed grades keep oak and satinwood from turning muddy.

Gathering the Right Kit

You need less than you might think, but what you have should be good.

• Shellac flakes in your chosen grade, plus a bottle of methylated spirits or industrial denatured alcohol.
• A glass jar with a tight lid for mixing, and muslin for straining.
• Cotton wadding and a closely woven linen or cotton cloth for the rubber.
• Raw linseed oil for lubrication — a few drops go a very long way.
• Pumice powder, fine abrasives from 320 up to 1200 grit, and a soft brush or tack cloth.

Mix a 2 lb cut — roughly 250 g of flakes to a litre of spirit — and leave it to dissolve for at least twenty-four hours, shaking occasionally. Strain it through muslin before use. For the final sessions, dilute to a 1 lb cut and the film will flow out far more smoothly.

Preparing the Surface

French polish will not hide poor preparation; it magnifies it. Remove old wax with white spirit and fine wire wool, then decide honestly whether the existing finish can be revived or must come off. Loose veneer must be glued and clamped first, and dents raised with a damp cloth and a warm iron before any abrasive touches the wood.

Sand carefully through the grits, always with the grain, and raise the fibres between passes with a barely damp cloth. On open-grained timbers such as oak and mahogany, fill the pores by working pumice powder into the grain with a little linseed oil and a coarse cloth, wiping across the grain and then along it. Colour should be corrected now with spirit stains — not afterwards, when a patchy finish is far harder to disguise.

Building the Finish

Charge the rubber sparingly. Too much shellac produces a wet, dragging pad that smears; too little and you polish the surface rather than feed it. Work in overlapping circles and figure-of-eight movements, keeping the pad constantly moving and lifting it at the end of each pass so it never sits still and sticks.

Add a single drop of linseed oil to the face of the rubber when it begins to drag. Oil is a lubricant, not an ingredient — if you can see it on the surface, you have used too much.

Build the body of the finish over several short sessions rather than one long one, letting each session dry for twenty minutes or so. When the grain is filled and the surface has an even sheen, switch to spiriting off: a rubber charged with spirit alone, used in light, quick strokes with the grain to clear the oil streaks and close the pores of the film. Leave the piece for several days to harden, then burnish with rottenstone or fine pumice and oil, and finish with a soft cloth.

Faults, Weather and Good Habits

Most problems come from impatience or damp. A cloudy white film — blooming — appears when the air is humid; work in a warm, dry room and it will not happen. Ridges and streaks mean the rubber was overloaded or moved too slowly. A tacky surface means too much oil was left behind during spiriting off.

• Never polish over silicone-based furniture sprays; they cause crawling that is very hard to correct.
• Keep the film thin. Thick shellac crazes within a few years and looks plastic.
• Work in good light, at an angle, so you can see the reflection and judge the surface honestly.
• Recharge the rubber often, but lightly — small, frequent charges beat one heavy one.

Learn to read the shine as it comes up and you will find that French polishing rewards patience more than talent. It is a slow conversation with the timber, and the mahogany usually gets the last word.