Fine Finishes for Wooden Stringed Instruments

One of the most important factors in choosing a wooden stringed instrument is the quality of the instrument’s finish. This is an instrument that you will be handling often through your life time and should hold up for a lifetime. Most crafts people will tell you the most important part of an instrument is in the selection of the woods for the instrument especially for the soundboard, backboard and the tuning pin blocks and then in the assiduous care given to the putting together of these elements. However I would contend that just as much attention should be given to its finish. In fact I spend as much time or more in the finishing of my instruments.

In a previous blog I described an ancient oil based finishing process which was most likely the type of finish used on wooden instruments for as far back as at least a thousand years and as late as 40 years ago. However because such finishes penetrate so deeply into the wood it makes it not as desirable a finish on modern folk instruments, because it has the effect of dampening the tone and sustain of wooden stringed instruments. For this reason I choose to use a topical finish.

The aim of modern finishes for wooden stringed instruments is a durable yet malleable seal which can withstand the natural movement of thin woods used for the soundboard and backboard in contrasting environments, but also for the stress of tensioned strings. The oil finish which I have described before have these durable and malleable characteristics as well and some forms of this method are a most desirable finish for hardwood floors for an example. Wooden folk instruments are not likely to be exposed to water and chemicals as are the finishes of floors or table tops in which the oil finish is so desirable.

In modern finishing of folk instruments special poly-vinyl lacquers have been specially formulated. They are durable but more importantly for wooden stringed instruments they have super elongation properties.

The most important factor in the finest of finishes on wood is the assiduous care in preparing the wood for applying a fine finish. I spare no effort in sanding my instruments with successive finer grits of sand paper. I may start with 80-100 grit sand paper whose primary purpose is to remove machine marks from planning or saw cuts. I do not go to higher grits until these marks or deep scratches are removed. Then 120 grit is used to remove the scratches of courser grades of sandpaper. All along it is important to sand with the grain of the wood. After 120 grit is finished then I apply 180 grit sanding. For curves and contours I often use 000 steel wool and then 0000 steel wool. I finish my fine sanding with 220 grit paper on most woods, but for more dense grades of wood such as Maple or Birch I finish with 320 grit paper.

After your sanding has been thoroughly inspected the wood must be vacuumed and then cleaned with mineral spirits to remove all the dust. When sanding in preparation for applying a fine finish it is helpful to remind yourself that with successive layers of finish you are going to be magnifying the flaws in the wood and especially the fine scratches and such you have failed to remove.

Before applying the finish to the instruments I prepare a place for this operation that is as dust free as possible. Also for using fast surfacing lacquers it is important to control as much as possible the level of humidity in the finishing space. Sometimes lacquer retardants or driers have to be very carefully added and thoroughly blended into the lacquer. As this is being done it requires applying the finish to test strips of the same kind of wood as the instrument until you achieve the desired results.

For applying finishing lacquers I use a gravity flow air sprayer and use test surfaces to adjust the spray pattern and make sure the best air pressure is set. There are some brushable type lacquers such as the brand Deft. I prefer not using this type of finishing material for several reasons. The lacquer has to be slower drying in order to be able to apply it with a brush, but it still dries relatively quickly so great care has to be applied to not over brush in spreading the lacquer or you get brush strokes in the finish which are very difficult to get out later. But the main reason I prefer not to use a brushable lacquer is that such lacquers contain pigment which reduces the clarity of the finish, but most importantly it reduces the solids content of the lacquer and in so doing it reduces its durability.

The first coat applied to my instruments is a lacquer sanding sealer that must be compatible with the specially formulated stringed instrument lacquer. My choice is Mohawk E-Z vinyl Sanding Sealer. The first coat must be applied evenly and completely seal the surface of the wood. Because the sanding sealer dries so quickly it raises the grain of the wood. After this step the sanding sealer has to be carefully sanded by hand with 220 grit paper and then 320 grit until it feels very slick to your hands. It has to be cleaned again to remove all the fine dust.

After this first coat and sanding I apply successive coats of sanding sealer rubbing down between coats with 0000 steel wool and cleaning fastidiously between coats. How many coats of sanding sealer that need to be applied has to do with the wood, especially open grain woods like Oak or even Black Walnut. The grain needs to be filled for the seal to be complete. There are wood grain fillers that are available to apply to these types of woods during the sanding process. I have been using Old Masters Wood Grain Filler for decades. It is available on Amazon. These are applied with a putty knife and a stiff brush going across the grain. When the grain filler dries I use a very sharp plane iron to scrap off the excess and then flat sand with the grain of the wood.

Once the wood is completely sealed then once again the sanding sealer must be fine sanded with 320 grit paper and thoroughly cleaned again.

The next part of the finishing is in applying the buildup of solid lacquer. My choice for this finish is Mohawk Classic Instrument Lacquer in clear high gloss.

This is the step in the finish when using an air siphon flow sprayer that you need to perfect the spray pattern for a wide even spray and adjust the air pressure for applying this type of finish. If not meticulous in these adjustments the results are either too fine a spray pattern or an orange peel effect which are very difficult to smooth out.

I apply at least 6-12 coats of lacquer, rubbing down with 0000 steel wool between each coat and cleaning thoroughly before the next coat.

The final coat is rubbed down with 0000 steel wool and then all the surfaces are fine polished using first, extra fine pumice stone powder. This is done using paraffinic oil which I put in a spritzer bottle and spray evenly across the wood surfaces and then applies the pumice stone powder with a cloth or salting it on to the flat surfaces. This process must be vigorous and the flat surfaces done with a block to polish evenly with the grain of the wood. After finished with the pumice stone the surfaces must be cleaned usually multiple times with rags saturated with mineral spirits and then clean dry rags.

After polishing with pumice stone then complete the process with rottenstone as I did with the pumice stone. This finely polished finish provides a patina that is as smooth as a baby’s bottom and aesthetically pleasing to the eye, but more importantly will hold up to the daily handling of the instrument.

An Ancient Tried and Proven Finishing Method

Having spent 40+ years in woodworking, including cabinet making, furniture designing and building and antique restoration I have discovered many different techniques in doing finishing. My finish of choice for fine furniture and antiques is in a built up oil based finish. This process is very time consuming, but results in a finish that last hundreds of years.

This process begins with choosing a naphthenic oil as your medium. My favorite oils are Tung oil and Linseed oil either alone or combined. Linseed oil is most readily available as boiled Linseed oil. If you are looking for a faster build up this oil would be a good choice. It gives a faster build up because the oil has already been boiled. The downside is it is softer and not as durable as Tung Oil.

On denser hardwoods such as Maple or Birch I make a solution of 2 parts Tung oil to 1 part raw Linseed oil. I blend these oils thoroughly then cut the solution by 1/3 with a solvent such as mineral spirits, turpentine or orange oil. For softer woods such as Poplar or Basswood I cut the aforementioned blend with ¼ solvent.

After having meticulously sanded the wood to be finished with increasingly finer grit paper and ending this process with 220 grit sand paper, I thoroughly clean the wood with vacuuming and then wiping it down with mineral spirits. It is very important to make your finishing area as dust free as possible.

When the wood is clean and ready apply the aforementioned oil solution generously with a rag. After all surfaces are thoroughly covered then take your hands and rub the wood vigorously until you feel the heat generated. Let the oil stand on the wood about 1 hour then wipe off the excess oil. You will then let the finish set overnight. After a minimum of 12 hours, then rub down the wood with 000 or 0000 steel wool and again thoroughly clean before applying more of the oil solution to the wood. On denser woods you will apply this diluted combination of oils an average of 4 times, rubbing it down with steel wool between each coat. On softer woods this requires 8-12 applications. The objective is to get as deep a penetration of oil into the wood as possible and to completely seal the pores of the wood. You will generally be able to tell when this has been accomplished, but when in doubt it is better to add more coats.

After the wood is completely sealed from the inside out it is now time to build up the finish for successive coats of oil. Make sure you have meticulously rubbed down your last sealing coat and thoroughly cleaned it as you have previously. At this point it is now time to cook your oils. I prefer at this point to use only straight raw Tung oil. Many of the products sold as Tung oil are actually diluted oil with mineral spirits. I have found two good sources for pure Tung Oil: www.realmilkpaint.com and Hope’s Pure Tung Oil on www.amazon.com.

It is important to heat your pure Tung oil slowly uncovered until it reaches a boil, then let it slow simmer for 20-30 minutes. At this point let the oil cool slowly. When it is room temperature pour it into a container with a good seal top. This is important because exposed to air the oil will harden.

Now it is time to apply the boiled oil onto the wood evenly with a clean cloth (I like to use t-shirt material). Let each coat sit a minimum of 24 hours, after which you rub down the coat with 0000 steel wool and as before clean between each coat.

Four such coats are adequate for most applications, but I almost always do more coats, especially for hard wear areas like table tops in which case I do 8-12 coats.

When you have reached your desired build up it is time for fine finishing to reach the desired sheen and patina. Firstly the wood is to be rubbed thoroughly with 0000 steel wool. It may take longer than 24 hours before starting this process. Make sure that when you are rubbing the surfaces with steel wool that the wool does not become oily.

Secondly, the surfaces are to be vigorously rubbed down with extra fine pumice stone powder. I spray my surfaces with a spritzer bottle containing paraffinic oil, usually found in lamp oil. Then apply the pumice stone powder to a clean soft cloth. For flat surfaces be sure to use a flat block to make certain you are rubbing the surfaces evenly and rub with the grain of the wood. Be fastidiously thorough with this process. On flat surfaces I apply the oil evenly and then salt the surface with the fine powder.

After you have accomplished this step wipe off the oily surface with a rag and then wipe again with mineral spirits and finish again with a clean dry cloth.

Thirdly the final finishing is done with Rottenstone which is super fine. You will use the same process as with the pumice stone.

This finishing process is the most durable of any finish I know and will literally last for centuries so it is worth all the time, expense and care it takes to do this finish. It withstands water and most chemicals. The wood remains unaffected by scratches of daily use because it has sealed the wood from the inside out, unlike topical finishes such as polyurethane or lacquer. You will never have to worry about condensation rings on the table top. For table tops which are cleaned weekly it is best cleaned with window cleaner or with ammonia and water solution. Other surfaces can be cleaned monthly with orange oil.

I went to the pains to describe this ancient finishing process for the serious woodworker or for the antique restorer, because this is an authentic process of finishing that goes back thousands of years. For ancient folk instrument crafts people this finish or a variant thereof would have been used in the finishing of their instruments even up through the 19th century. I have seen 300 year old violins finished with oil finishes and 40-100 year old Appalachian folk instruments done in this fashion.

All that having been said, I go further to say this is not the best finish to use on modern wooden stringed instruments. The simple factor for not using this method is that this method so thoroughly seals and finishes the wood that it dampens its sound and sustain.