I recently went on a French polishing course and I took a few notes while I was there. What follows below are the notes I took typed up neatly so that I don’t forget everything. Some of it might be a bit disjointed but there are some gems in there and it’s in roughly the order you need to complete the steps. The guy teaching the course had 40+ years experience and there was literally nothing he didn’t know about finishing wood.
Finishes can be split into four basic groups:
- Water based e.g acrylic floor sealer
- Oil based e.g exterior varnish
- Nitrocellulose based e.g. spray lacquer
- Spirit based e.g. French polish
There are no hard and fast rules regarding compatibility. It depends in factors such as how long the previous coats have been left to dry, humidity, temperature, thinners used, etc, etc. A test piece should be made up if possible.
Applying a second coat of a finish will sometimes partially dissolve the first coat of finish. If this is a problem a sealing coat of a different type of finish can sometimes be applied over the first coat. The partial dissolving of the first coat is sometimes desirable as with French polishing where it allows for the build up of a thicker finish.
French polishing doesn’t produce a hard wearing finish. It is easily damaged by solvents (including alcohol), water and heat. Some newer shellacs have additives which make them more resistant particularly to heat.
Shellac can usually be applied over water and oil based stains and fillers including chemical stains. It’s generally a bad idea to try and use spirit based stains under French polish as the spirit in the polish will lift the stain causing a patchy finish. If the shellac needs to be coloured spirit based powders can be used. Earth pigments can also be added to the shellac to change the colour.
Solvents and Type
|White Spirit||Oil||Also known as mineral spirit and turpentine substitute. Easily available from DIY stores.|
|Naphtha||Oil||Similar to white spirit but harder to get hold of. Good general purpose oil based solvent.|
|Turpentine||Oil||Distillation of resin from trees. Good general purpose solvent.|
|Acetone||Cellulose||A good light solvent. Low boiling point so it evaporates easily. Very flammable and can easily produce explosive mixtures in air.|
|Thinners||Cellulose||A range of solvents often used for spray finishes. All are highly flammable and some are moderately toxic.|
|Acrylic||Water||Acrylics are a range of water soluble organic chemicals which when dry polymerise and become water resistant. Generally considered some of the safest finishes.|
|Ethanol||Spirit||Commonly referred to as alcohol (even though that is a whole group of chemicals) this is the same as the stuff you drink. Pure ethanol is usually hard to get hold of and expensive due to taxes. A boiling point of 78 deg C means it evaporates easily.|
|Methanol||Spirit||A member of the alcohol family. Highly toxic by ingestion and can be dangerous through inhalation in confined spaces. Not commonly used. Also known as wood naphtha.|
|Methylated Spirit||Spirit||Ethanol with small amounts of other chemicals added to denature it. In the past methanol was added (hence the name) but that has somewhat fallen out of favour due to toxicity of methanol. A purple dye is usually also added. Generally referred to as meths.|
The steps discussed below are in the order you want to apply them to the job.
It is still possible to get dichloromethane (DCM) based paint stripper if you are registered as a business. It’s far superior to all other formulations of paint stripper. Lay the stripper on thickly and let it soften the finish, typically a few minutes. On flat areas use a flat scraper to remove the finish taking note of the wood grain. Repeat if needed. Clean off using 000 wire wool and cellulose thinners (e.g. spray gun wash), this will help remove any stubborn finish and neutralise the stripper..
For areas with carving or molding paint the stripper on thickly and wait a little longer for it to work. Just before it dries out brush it in circular motions. The stiffness of the bristles is key to this working. Too soft and they wont lift the old finish, too stiff and you risk damaging the carving. When done wash the whole area down with cellulose thinners and 000 wire wool brushing if needed.
For large flat areas a random orbit sander with a fine grit can be used. For more delicate or curved areas 240 grit Abranet by hand is best. Wipe off excessive dust with a soft cloth dipped in thinners. For tricky areas dry 000 wire wool is good for preparing the surface.
Removing Stains – Oxalic Acid
Black stains caused by hot cups, plant pots, etc can often be lightened using oxalic acid. This process must be carried out after all the old finish has been removed. It can also rejuvenate rain damaged and external timbers. Works best on woods that contain a lot of tannins such as oak.
Mix oxalic acid crystals with water or meths and apply to the stained area. The amount of time it takes to work can vary considerably from almost instantly to hours. It can be applied multiple times to improve the result. When satisfied it must be neutralised by washing off with water or meths.
If damage to the piece is too deep to sand out it can be filled with essentially any filler that will take a stain. Getting a good colour match isn’t terribly important as the match will be made later during French polishing. Aim for a lighter colour than the surrounding wood since it’s easier to darken the filler than lighten it. Most fillers have a light pine type colour which is generally all that’s needed.
If earth pigments are available they can be mixed with the filler to better match the colour of the timber being worked on. Brown and black are generally all that’s needed. Getting a better match at this stage can save a little work later.
Grain filling is carried out on bare timber before any stain is applied. It is a type of stain itself but it’s primary job is to stop subsequent stains and finishes from soaking too deeply into the wood. This results in a better finish and more control over the staining and finishing process. Oak is often grain filled but it’s not strictly necessary, mahogany almost always requires grain filling to get a good finish.
Grain filler should be applied with a cloth and then wiped off before it dries. If it dries it can often be hard to remove other than by sanding (thinners will sometimes work). Grain filler can sometimes be thinned with thinners and brushed on but obviously that will reduce it’s effectiveness.
Hit the wood with stones or chains. Various sizes, shapes and textures should be used to give a naturally aged look. This process should be carried out before any stain is applied.
Staining and Colouring
Powdered dyes that are highly soluble in meths. Can be applied to the wood or mixed in with the shellac to create a coloured finish e.g. black shellac can be used for ebonising. Most useful colours are Bismark brown (which is red), green, yellow and black.
By careful selection of dye colour it’s possible to match together quite starkly different coloured woods. If the wood is too red it can be toned down with green or yellow, this is good for matching sun bleached wood and can also give the piece a more antique look.
Bought as crystals which can be dissolved in water to make a purple solution. Used to darken oak chemically, will work on other tannin containing woods as well. Apply using French polishing wadding or similar, discard once complete.
Pine is generally difficult to stain well. Water based stains are best as they will minimise the blotchy appearance that is common with stained pine.
Staining large areas quickly is best done with naphtha based stains. Typically reserved for unseen areas that just need some colour e.g. inside of draws, backs of cabinets. The colour is usually uniform and dull. Don’t forget this is an oil based stain when applying the next coat.
Essentially just crushed up rock. Earth pigments aren’t soluble in anything but they can be mixed with waxes to enhance colour and other thick materials like fillers to colour match. Brown umber is a commonly used colour.
Van Dyke Crystals
Mix crystals with warm water and, if possible, leave to stand for a few days to mature. Aim to mix stronger than required and then dilute to the preferred strength. The mixture will keep for a long time if stored with a sealed lid.
Brush the mixture on and work into the grain. Wipe, don’t rub, off with a dry absorbent cloth until the desired look is achieved. If the stain is too dark wet a rag and rub gently to remove some of the colour. This lightening technique can, for example, be used to make the edge of the piece dark and then fade towards a lighter centre. Note that moldings are naturally darker than other areas of a piece. Lightening of a Van Dyke stain can be done at any point until it’s finished. It will re-wet even if completely dried.
If more lightening is required than can be achieved using water alone pumice power can be used to lighten a Van Dyke stain further. The amount of lightening achieved in this way varies.
If a piece has inlay that you don’t want to stain, for example mother of pearl, simply paint over it with a clear shellac solution before proceeding with the staining. The stain will then wipe off once it’s dried on the rest of the piece.
French Polishing Mop
A French polishing mop is basically just a paint brush but with very soft bristles (squirrel hair is often used). A good mop is expensive but if looked after it will last a long time. A number 12 is a good general purpose size and suitable for small to medium large pieces. Mops can be washed out after use in meths or stored with the bristles in meths. The advantage of a mop over a rubber is speed – in three or four coats a mop will apply what a rubber will take twenty or more coats to apply.
French Polishing Rubber
A French polishing rubber is a small ball or boat of soft, lint free, cotton rag with cotton wadding inside. A ball shape is best for delicate areas a boat shape for larger flat areas. The rag should be formed tightly around the wadding inside. Wadding with an interfacing material can bought which helps to prevent fibres from the wadding making their way into the finish.
There are a wide variety of shellacs now available with various attributes such as heat and water resistance.
White shellac is the most basic and is clear and not very hard wearing, shellac sealer is a alternative. If covering a stained surface a transparent shellac is usually best.
Button polish is the most commonly available shellac. It’s name comes from the fact it’s often sold as buttons of shellac. Buttons are dissolved in meths to the required strength. Typically button polish has a yellow to green tint which can give the piece a more antique look.
If the piece can accept a little colour a good base coat is Morrells Pale Polish, it’s slightly heat resistant and goes on easily. If absolutely no colour should come from the polish then a white polish must be used. The as-bought shellac solution is usually a little on the strong side and should be diluted with meths before use.
Dip the mop in the shellac solution , wipe off the excess and brush onto the piece using a smooth wiping motion. Apply three or four coats using the mop to build up a good base layer of shellac. After the first coat sand lightly with a fine paper (e.g. 400 grit) and wipe off excess dust. Sand again after the third or fourth coat and again wipe off. If the finish rips when sanding either the paper was too coarse or the finish hadn’t been given enough time to dry.
If the piece has been repaired with filler stop mopping after the second coat and colour the filler to match the rest of the wood. Use earth pigments in shellac to match the colour as closely as possible and then apply with a very fine artists brush to just the filled area. Leave to dry before apply at least two more coats with the mop.
Once the piece has thoroughly dried knock it back hard with a fine (400 grit) sand paper. Completely remove any shine from the piece but take care not to sand through the finish. The initial mopping on of the shellac fills any pores in the wood and builds up an even thickness surface. The sanding back then levels the surface ready for the final coats.
Make up a rubber and load it with polish. Apply the finish with a smooth wiping motion. Don’t slow or stop as the rubber may stick and damage the surface. Apply four or five coats this way.
Finally, rub the piece all over with fine wire wool 000 or 0000 to produce a mat finish. Using a fine brush apply a good quality clear light bees wax (Fiddes do a good wax). If necessary some waxes can be thinned a little with white spirit, ideally wax will have the consistency of very thick paint. Earth pigments can be used to colour the wax, this is useful for killing any dust that may have become trapped in hard to reach areas – brown and black are most useful. Wipe off excess wax with a cloth and then using a clean cloth buff to a high shine.
If a piece needs refinishing and it has been waxed the wax can be removed using a little white spirit and fine wire wool.