...On Varnishing a Violin
I have often been asked how to varnish a violin, and here I present one approach to this very diverse subject. I have experimented with a number of materials and techniques over the years, and this represents only one interesting possibility that I have worked with recently, and which offers room for further developement. I have an interest in using local materials as much as possible for the individual character it gives to the instrument, and for the intimacy it gives me with the work. This method features the use of propolis and wax obtained from a local beekeeper and resin gathered from the forest around my home. With a bit of experimentation, it could be adapted to utilize other locally accessible materials.
Propolis is a brown resin-like material that honey bees produce to patch up little holes and cracks in their hives. I separate it out from the wax and debris by first soaking it in warmed alcohol to dissolve the wax and pour it off. Then I wash it again in warm water to skim off the broken bee parts and other impurities and separate out the propolis that sinks to the bottom. The "soap" is made by dissolving the propolis in a solution of lye (you can just use the sodium hydroxide from the grocery store), filtering it, and then combining it with a solution of alum (aluminum potassium sulfate). The "soap" will precipitate out of solution and the wet mud that you get when you filter it is the good stuff. This recipe is adapted from one by California violin maker Bill Fulton.
Rosin oil is distilled from pine resin -- when the raw stuff that drips from an injured tree is processed, it is first heated to distil off the more volatile turpentine, leaving behind the more solid rosin. When the rosin is further heated, it gives off another fraction that can be condensed as rosin oil. It has several grades, depending on what temperature and stage of the distillation breakdown of the rosin it is drawn at. I use a middle grade. Rosin oil is thick and heavy, but it is extremely penetrating -- it will soak right through the curly grain of the ribs. It has good matching of refractive index with the wood and varnish, and by soaking in and surrounding the sealer and wood, it gives nice depth and transparency to the grain. It can take a few days to dry, but light will help speed the drying. It goes on like an oil, but will dry rather hard and resin-like.
The Canadian balsam fir produces a resin that can be gathered from small bubbles or blisters that appear on the trunks of the trees. This resin or balsam that is found just inside the bark is produced by the tree as a defense mechanism -- it will quickly seal off against infection any injury to the outside of the tree. Unlike a pine or many other resin producing trees, it will not run or "bleed" from an injury; it must instead be tediously gathered a drop or two at a time from the blisters themselves. The balsam from the Austrian white fir, known as Strassbourg Turpentine is a well known high quality resin traditionally used by artists as a painting medium and varnish. The Canadian fir produces a similar resin that can be turned into a fine violin varnish. It must first be cleaned by filtering it warm to separate it from the dirt, bark, and insects. So as not to waste any, the bark and other residue can be further cleaned by soaking it in warm alcohol -- the liquid can be poured off and cooked, evaporating off the alcohol and leaving the purified balsam behind.
Linseed oil (from flax seed) is one of a number of "drying" oils which will turn from its oily state into a tough and durable film upon exposure to light and air (other examples of drying oils are tung, poppy, walnut, and hempseed oils) This happens through a process of oxidation (taking on oxygen from the air) and polymerization (the molecules link together into long chains, rather than floating freely as in a liquid state.) Because of this ability to form a tough yet flexible film, linseed oil has long been used in painting mediums and protective varnishes. For varnish making, the oil can be "bodied" or thickened beforehand by gentle cooking, exposure to sunlight, or by blowing air through it (a small aquarium bubbler works well). The pure raw linseed oil can also be processed simply through the cooking involved in making the varnish itself.
A traditional oil varnish is basically a combination of a resin and a drying oil. Cooking them together helps them to "co-polymerize" into a usable varnish. By varying the proportions and the cooking process, different qualities can be encouraged in the varnish -- brushing and drying characteristics, color, hardness and flexibility. I have been using two distinct varnishes -- one for the color coats, and one for the protective top coats. To make the varnish, I start with the raw filtered balsam as described above. It is placed in a stainless steel pan to cook it and drive off some of the more volatile "oily" elements, leaving behind a resin that will solidify upon cooling. All varnish cooking should be done in small quantities, outdoors (lots of fumes) -- and be prepared for fire. For the clear top coats, I cook it just enough so that it will solidify into a light rosin-like consistency. For a richly coloured red-brown varnish, I continue cooking until it is considerably reduced in volume and the resin looks almost like black tar in the pan. Linseed oil is then added in equal or slightly greater volume and the two are cooked together. More oil will result in a more flexible film, lighter in color; less oil will tend to a more brittle, darker varnish, and a harder to manipulate. Longer cooking and higher temperatures will make a faster drying varnish, but can be harder to brush out nicely. I usually cook the varnish until a small drop, pinched between the fingers, can be drawn out into a long spider web like strand. However, I cook varnish much as I cook in the kitchen -- I don't use a precise recipe, but rather judge things as I go as to how much, how hot, how long,. Keep a constant eye on it and keep in mind the particular qualities that you desire for for the batch you are cooking. To finish the varnish, it is allowed to cool somewhat, at which point turpentine can be added as a thinner to bring it to a usable brushing consistency. It should be filtered while still warm and thin, and then allowed to sit and settle on the shelf before using.
Driers and Retarders:
If you cook your varnish properly, it should have no problem with drying, but ultraviolet light is key to curing the varnish. The UV speeds up the polymerization of the oil molecules, which are now bound to the resin. When a varnish dries, first the turpentine -- which is there just to thin it and make it more brushable, sprayable or whatever -- evaporates off, and then the oil/resin varnish itself oxidizes and polymerizes into a tough film. Without light, the varnish may take weeks to dry, rather than overnight. Sometimes varnishes will use heavy metal dryers (lead, cobalt, etc.) to speed up the oxidation process, but these can also cause problems if not used carefully. I avoid using artificial dryers, and instead rely on proper cooking and sufficient exposure to (ultraviolet) light. I have a cabinet outfitted with ultraviolet bulbs, but good direct sunlight (even a pane of glass will filter out a lot of UV) is best -- if you can keep the dust, rain and flies out. I will sometimes use a bit of clove oil for the opposite effect -- to slow down the drying when I find that a varnish gets a little too sticky too fast, making it hard to brush out evenly. Clove oil is a volatile solvent, like turpentine, but much slower to evaporate, so by remaining in the varnish longer, it allows you a little more time to manipulate the varnish before it gets too tacky. It's good for dark color coats where it is important to try to brush them out nice and thin and even. If needed, it should be used sparingly -- just a few drops, and plan to let it dry a little longer. Smells nice!
Scrape/sand the instrument down for the kind of surface texture you want. I like to leave the top grain raised and textured to accentuate the reed, so I don't use any sandpaper on the top (except maybe a little just around the very edge). The rest of it I like to polish off fairly smooth, so I'll scrape, perhaps give it a bit of fine sanding, wet it down to raise the grain, then smooth it down again, and perhaps repeat. The scraper leaves cleaner lines and surfaces, so try to avoid any more sandpaper than necessary. The top also will be wet down and the grain allowed to swell -- it can then be similarly smoothed off; to a greater or lesser degree or left with lots of grain texture and character.
Start with a strong solution of tea -- several bags in a half cup or so of water; boil a few minutes and steep. when it's cooled down enough, remove the bags, filter if necessary, and wipe it all over the instrument -- don't forget the inside edges of the f holes. This alone can give a gentle golden orange hint to the wood, but if a deeper and darker tone is wanted, it can be placed in a closed container (sealed garbage bags will do) with a cup or so of household ammonia and left exposed to the fumes for up to a few hours. The tannic acid from the tea will react with the ammonia to darken the wood without the problems associated with a dye or pigment stain. You can check on the color -- it gets darker with longer exposure. Don't worry about the green-grey color it may take on-- the red tones of the varnish will take care of that. After it airs out and doesn't smell any more, give it a coat of the propolis ground. Rub it vigorously into the wood -- use a cloth to burnish it in. It will take on a gentle polished look. You don't want it to build up on the surface, just absorb into the wood and fill the pores. The surface will take on a dusty, opaque appearance, but the next step will clear that. After it's dry, give it a coat of the rosin oil -- it will penetrate the wood and surround all the particles of the ground and you'll see the depth and transparency of the grain restored. Let the oil dry in sunlight to speed it along. Check especially the top to see that it has taken on a shiny appearance indicating that the surface has been sealed. If there are dull spots, you might give it another coat of rosin oil just to make sure. When you are satisfied with that, give the violin a rubbing down and burnishing of the surface to smooth it in preparation for the varnish itself.
When the surface is sealed and prepared with the ground, you can start the color coats without fear of the dark colours contaminating the wood, which can otherwise make it end up end up looking blotchy and uneven. At this stage, some makers will use pigments to achieve the desired color -- you can use artists' colours from the tube, or you could even try making your own "lake" pigment from madder root (for a traditional Cremonese red). These pigments, ground in oil, can be glazed directly onto the instrument -- work it into the surface with a soft brush, and even better, your fingers (just go lightly and seal it in with a thin coat of varnish -- repeat if necessary) or they can be added into the varnish to enhance its color. However, I have been happy to forgo the use of added pigments, instead using the dark cooked resin varnish to give me the depth of color I want. When judging the color, be careful of your light conditions -- there is a huge difference in appearance whether you are using direct or indirect sunlight, incandescent or fluorescent bulbs, etc. In general, I think it's better to try for a lighter, more transparent finish, than risking obscuring the grain with too dark a varnish. Use thin coats of varnish -- more thin coats are better than fewer thick ones -- add a little turpentine if needed. Brush it out thin and smooth (try to work fairly quickly, and don't overbrush) You can shade it in, giving it shadows and highlights, or just try to lay it on evenly all over. You'll probably give it at least several coats. I might use up to four or five in the "shadow" areas, while avoiding entirely the highlights. For the top, with its raised grain, I brush it on quickly, then immediately wipe it off with the palm of my hand, rubbing it into the wood. This causes it to collect somewhat in the reeds, thus accentuating the grain of the top. Try not to sand between coats -- the thin coloured coats want to remain intact for their evenness of color. Try not to let too much dust, hair, and flies accumulate in the surface. Wiping it all off with a sticky tack cloth before varnishing helps, and don't do it when your shop is full of dust.
When you've got the color you want, it's nice to give it a couple of coats of clear or light varnish to seal everything in and give you a surface that you can polish a bit without disturbing the delicate color coats underneath. I usually give it two coats, and then sand it down with some very fine sandpaper (1500 grit or finer) . Just be careful not to go through your top coats and into the color coats. This is where your original surface preparation helps. Try to gently sand out any little dust nibs, brush marks, and such. For a deeply textured top, I might skip this sanding altogether -- it's too easy to wear through the raised grain lines. Just give it a light top coat and try your best to keep it clean. Smooth off the rest of the surface as much as you can, and then give it all one final clear coat. When this has dried well, you can rub the whole instrument down with a bit of fine pumice and oil (I use linseed oil), and if again, try to avoid cutting through that final coat. Finish off by rubbing it with just a hint of bee's wax cut with oil and turps -- buff it in with a coarse cloth, and don't let it build up on the surface. You can use rottenstone and finer abrasives to really bring up the gloss, but I prefer to leave it a little duller and softer looking, and let time do the rest.
When varnishing, probably the easiest mistake to make is to lay on too much varnish.-- it's not good acoustically or in terms of appearance. Good initial preparation means you can get away with less varnish and still be able to polish the surface the way you want. It's probably better to leave the varnish thinner, and the surface a little more textured, than to keep adding coats of varnish trying to level and polish it all out afterwards. A good ground coat helps here and this is why it is common to use a ground that is high in mineral content -- the particles help plug and fill the pores and smooth the small surface imperfections. The alum in the propolis ground helps to do just this.
The painters' rule of thumb is "fat over lean", meaning that as you build up from the surface, you should use a greater oil content in your top coats than in your lower ones. This helps avoid cracking and wrinkling of the surface. Better yet, keep your coats thin and varnish buildup minimal, and always let it dry thoroughly between coats.
Lots of other materials and techniques can be used successfully. I enjoy working with these materials, and I have learned to adapt them to my needs. I make no claims for historical precedence or accuracy, and I would encourage anyone to experiment, and to learn from one's own experience and judgement.