Friday 3 July 2020

Building a 13 Course Lute, Start to Finish, 18: Making and Applying Varnish

Hi my friends--I hope you're well. It has been a while since I posted, so let's get to it. Today I want to talk about my varnish: what it is, how I make it, and how I apply it to a lute.

A selection of varnish samples on various kinds of woods (honduras rosewood, curly maple, yew, and ash.) I make a varnish sample to go along with every lute that I build.
First, a note of caution. The process of varnish making that I'll be talking about today can be quite hazardous if proper precautions aren't taken. I don't think anyone should attempt to make this varnish without being properly trained. Please don't use this blog post as a 'how-to' for varnish making; it's a description (and not a very complete one), not a set of instructions.

The stuff that I make and use is a terpene resin varnish that's commonly called Fulton Varnish, after the person who formulated it, William Fulton, an aerospace engineer, violinmaker and varnish researcher and experimenter. Fulton published the results of his work in a series of articles in The Strad in the early 1970s; I was introduced to his techniques by Grant Tomlinson in the early 2000s. Grant had been working with Fulton's recipe for years, so by the time I came along he had worked out pretty much all the kinks (and there are a number of kinks that needed working out.)

You may have heard of modern violin makers' search for the 'Secrets of Stradivarius,' the lost methods of the old masters that, if only we could recover them, would allow us to build violins with the magical soul of the old instruments. High on the list of 'secrets' is the oil varnish used by the old Cremonese masters. Of course, varnish alone won't make a great violin (or a great lute), but if it's a good varnish, it will do a few things: be beautiful, in finish, lustre and colour; be stable over a long period of time; and be reasonably simple to make and apply. Fulton's varnish fulfills all of these requirements.

The old makers' varnish is not exactly a 'secret,' in the sense that it's somehow being purposely hoarded or withheld. It's simply a recipe, or more accurately a technique, that's been lost over the centuries, supplanted by the products of the industrial age. Mass-produced finishes took the place of the old and locally-made, even shop-made, varnishes. By the time instrument makers realized that these newer products might not be--ahem--all they were cracked up to be, the old techniques of making oil varnish were mainly lost. Human cultural memory is short.

Many old recipes for making oil varnish survive, but Fulton took seriously the idea that the ingredients named in them might not be quite the same stuff as their modern equivalents. For instance, one of the main ingredients in some of these old recipes is 'turpentine.' When I say that word, you may think of the clear, distilled liquid thinner for paint and varnish. But Fulton realized that the turpentine of 300 or 400 years ago would have been very different: more contaminates and oxygen in the mix, gummier, thicker and browner, more like the sap of the coniferous trees from which it had been derived.

So Fulton decided to take the modern distilled spirit of gum turpentine, and turn it back into the turpentine of 3 or 400 years ago, by oxygenating it (bubbling air through it with an aquarium bubbler) and exposing it to ultraviolet light (in the form of sunlight) over a number of weeks or months. The result of this back-engineering is polymerized terpene resin. Here's what it looks like in a gallon jar:  dark brown in colour, and about as viscous as blackstrap molasses.

Some of the turpentine evaporates during the polymerization process. The piece of masking tape shows the original volume of turps in this batch, so you can see that I'm left with less than half the original volume.
This particular batch of polymerized turpentine was made not by me but by Grant Tomlinson, and had sat high up on a shelf in his workshop for many years. Over the time I've known and worked with Grant he's shown me many techniques of the lute maker's craft, but few as valuable as varnish making. I first assisted him making a batch of varnish in 2005; then in 2010, Grant assisted me in my own first attempt. Last September, when the picture above was taken, I attempted to make Fulton varnish flying solo for the first time.

Now I said above that Fulton's varnish is reasonably simple to make, but that doesn't quite mean that it's easy to make. For one thing, the cooking process creates some pretty noxious fumes, so it must be done outdoors. This, in turn, creates some logistical problems, such as where to cook and when. When I made varnish with Grant in 2005 and 2010, we made it in the parking lot of the building next to our shops. This worked fine until a couple of summers ago when Grant was showing our colleague Wilma Van Berkel how to make varnish. That Sunday, I recall, was a beautiful day, with a slight breeze, which cleared away the fumes quite nicely; but unfortunately they were blown pretty directly toward an apartment building nearby, and partway through the cooking process an alarmed resident came over to see what in the world was going on, and whether she should call the fire department. I figured that this time, I should try to find somewhere more remote to do my cooking.

As for when to cook, since it is done outdoors, a clear day (or at least one without rain) is a necessity. In Vancouver, the end of September pretty much marks the end of decent summer weather; temperatures turn colder after that, and soon the rain--the torrential, unending months of it--begins. The window of time for me to do this cooking was running out fast. If I didn't do it soon, I would have to wait until spring.

I called my friend Bob, who has an acreage in Langley, about an hour out of town, and asked if he would host me. I warned him about the fumes, and he said it would be no problem, he wouldn't mind a bit.

So one Saturday morning in September I woke up, checked the weather forecast, and decided it was time to go. I drove to my workshop, loaded up my equipment, and headed out to Bob's. Here are some highlights of my varnish making day.

The full scene at Bob's beautiful acreage. I'm set up quite far away from a couple of houses on his property. You can see a yellow extension cord running to my work site from the outdoor kitchen a few feet away.

Here is the basic set-up. A milk crate provides a handy box for carrying equipment, and provides me with my seat. On the plywood, there are a hotplate; a cast-iron pot for cooking the resin; a pot lid for checking varnish hardness and colour; a pair of neoprene gloves; a heat diffuser for the hotplate; a lab thermometer (that reads to 400° C); and the jar of polymerized gum turps. Closer to the camera are wet towels, in case of emergency; and a tub of water, the presence of which I'll explain in a second.
On this day, my varnish making is divided into two parts. First, I must heat the polymerized gum turps to a certain temperature in the cast iron pot to make a brittle resin. I begin by pouring the gum turps into the pot, and heating slowly, stirring with the thermometer and keeping an eye on temperature. Around 125°C, a reaction takes place in which some volatile substances in the turps cook off, in the process creating a considerable amount of heat. This exothermic reaction can cause a rapid (and potentially dangerous) rise in temperature, as well as the creation of some heavy noxious gases. The tub of water in the photo above is available in case the reaction gets out of hand: I can lift the pot from the hotplate and dip it into the water to lower the temperature quickly.

In the event, there was very little exothermic reaction created by this particular batch of gum turps. I think one of the reasons why is that the batch was made long ago by Grant Tomlinson (he figured it might have been made twenty years ago), and it had simply mellowed, the volatile substances having dissipated over the years. Another possible reason why there was not much of a reaction is that the batch was not made using a certain chemical--manganese napthenate, to be specific--which Fulton recommended using as a catalyst in the original polymerization process.

Once past that rather tense phase of cooking, I could pretty confidently take the temperature of the gum turps slowly higher, ultimately somewhere above 300° C, the temperature needed for making a beautiful amber-brown shade of resin. (Lower terminal temperatures are used to create lighter-coloured resins and varnishes.)

Here I am, your humble narrator, enjoying the cooking process on a lovely late summer day.

This photo is courtesy of Bob, my host, who took a break from driving his tractor and cutting the grass while I made varnish. 

Here is the result of the cooking the resin, after removing from heat and allowing to cool. Although it looks like a liquid, it is a solid--I've converted the gum turps to a brittle resin.

Now I just need to remove it from the pot, which I do by breaking it up with a hammer and screwdriver. I will use some of this brittle resin for the second stage of my cooking day, where I actually cook varnish. The rest of this brittle resin I will put into a jar and keep until I need to make varnish next--which hopefully won't be for a few years. (The brittle resin will keep indefinitely.)

The varnish-making part of the day can now begin. I crush a certain amount of the brittle resin in a mortar, and mix it in another pot with stand oil. Then I heat this mixture steadily, over the course of about an hour, to around 300°C.
I don't have any photos of this part of the process, because I was busy doing it and paying pretty careful attention, and Bob had left the area. But here's what happened. I sat beside the hot plate, stirring constantly with the thermometer, taking temperature readings every minute and jotting them down in my notebook. Even small variations in the rate of heating, as well as the amount of time the varnish is held at the terminal temperature, can make differences in the quality of the varnish. I keep careful records of the cooking process, in the hope of tracking down the origins of these subtle differences.

Fulton's recipe calls for holding the varnish at the terminal temperature 'until a firm pill stage is reached.' I'm not exactly sure what he means by that, but here's what Grant taught me to do: take the thermometer from the pot and let a drip of varnish fall onto the cold pot lid. Let the drip cool for a few seconds, then tap it with your fingertip and lift away. The varnish will stick, and you'll pull away strands of beautiful amber varnish that billow and drift in the breeze. The longer you hold at the terminal temperature, the finer and longer these gossamer strands will become.

The Sorcerer's Pot-Lid. Who can tell the varnishes it has known!
And then, when you judge that the varnish can become no finer, you take it off the heat and let it cool. You can't keep heating indefinitely; your varnish will gel in the pot. That's about it. When the varnish has cooled to below 150°C, you can add some distilled spirit of gum turps as a thinner, and then filter into jars. Here is the final product.

It's lovely stuff. Can't wait to make a lute, and slap on a coat or two.

Which leads us to the next part of today's post: applying the varnish.

For this part of the process I decided to make a series of short videos on my phone. This marks a first for The Lute's Progress: I've never done a video demo before. I don't want to get your hopes up or anything--they aren't the highest of fidelities, I'm not used to talking to a camera, and my framing of the shots may leave a little to be desired. (For instance, in none of the videos can you see my face clearly. That may be either a glitch or a bonus feature; I'll leave it to you to decide.)

But I couldn't think of a better way to illustrate what I was doing in flattening off the previous varnish coat, and then brushing on the next one. It's not a process that lends itself to taking a bunch of photos, as I usually do, then writing descriptions. So, with all their faults, I humbly present these videos and hope that you can get a reasonably clear idea of what I'm up to when I apply a coat of oil varnish.

And that will be that for this time. Next time, I'll tell you about making the peg box. Cheers!

Video #1: Removing dust particles

Video #2: Flattening off the varnish

Video #3: Brushing varnish on the first few ribs

Video #4: Brushing varnish on the last ribs and capping strip


  1. This is very interesting stuff, Travis - keep it coming! What kind of brush do you use? Do you find it helpful to use a bigger brush for broad-ribbed instruments? I'm assuming your varnish has a fairly slow set, so you can take your time? I have lots of questions, but that will do for now...

  2. HI Martin, the brush I use in this demo is a Kolinsky Sable brush from Daniel Smith, no 10 or 12 I think (about 1/2" wide.) I also have a wider sable brush about 3/4" wide for wider ribbed lutes and guitar/ vihuela. They're wonderful brushes, and I've been using both for years. (I take a lot of care to clean them well after use.)

    The varnish flows so well, however, that I'm not sure you need to use a brush this good! I once read an interview with Fulton where he says just this, that pretty much any old brush will do. I like using a fine brush though, because I feel it gives me the best chance of success.

    And then there are the "cool kids" who spread the varnish on with their hands... Haven't tried that yet, though it looks like messy fun. I think if I were to do it this way, I'd have to mask off the neck. With a brush, you don't have to do this.

    The varnish does have a fairly slow set, but as I say in the video as I'm working, once I brush out a section well I can start to feel the brush pull harder, and then I know it's time to move on. It becomes a bit of an equation of brush width, rib width, and varnish viscosity (i.e., how much turps as a thinner has been added.)

    Other questions?

  3. Hi Travis,

    I'm a amateur luthier from spain. excuse my poor english!

    I ve a (very modest) blog of lutherie too:

    I follow your blog with attention, waiting for new entries, always interesting.

    Your barnish.. can dry without UV light treatment?

    I use shellac barnish (in spanish guitar tradition), but I think its anacronic and I'm thinking about use barnishing method like you!

    Ive some questions about you establish the height action of strings:

    In a previous entrie, you say that you use a little piece of wood of 1,6 mm height first fret for measure the height in 8 fret. You put this on 1rst fret position.. You use the same height for the rest of strings?

    Thanks in advance, greetings!

    1. Dear 'Unknown'... Thanks for your comment and question! This oil varnish must be dried using UV light. I use a cabinet with UV bulbs, and I leave two full days between coats for the varnish to dry. You can use direct sunlight instead, though you'll need to leave it in the sun for at least a week to get the same effect.

      About the height of strings--for this lute, when I am setting the action I use a 1.6 spacer at the first fret for all strings--this ensures that I am comparing the height of all strings from the same baseline. Down at the 8th fret where I measure the height of the string, I look for each course to rise about 0.1mm higher than the one before it. So, for instance, the first course might measure 2.7 at the 8th fret, and the 2nd course might be 2.8, the 3rd 2.9, etc.

      I hope this answers your questions!

      Best, Travis

  4. A great post, thanks Travis!
    May I ask why you use Stand Oil over cold pressed Linseed Oil?
    And how much turpentine (by ratio) do you tend to dilute the varnish with once it has cooked?
    Thank you!

    1. Hi! In his various writings about making this varnish, Fulton talks about using linseed oil that is 'break free,' i.e., which has been heated to 300° C and held there for 20 minutes to remove 'breaks' or impurities in the oil. This is basically a description of Stand Oil, so I use it to eliminate that step in the process.

      I don't know what the ratio of fresh turps to varnish is when I mix it together after cooking the varnish--I simply use Fulton's suggestion of 250cc. The consistency or viscosity of the final result does vary a bit, and I've found that when I get back to the shop, or rather when I'm preparing to use the varnish on some samples, I often find that the varnish needs a bit more dilution with fresh turps to bring it to a brushing consistency that I'm happy with. So I don't think that the precise amount is all that important (and as Fulton notes somewhere in his writings, if you happen to add too much fresh turps, all you need to do is put the varnish in a pot and cook it a little to evaporate some of the turpentine, without hurting the varnish at all.)

  5. This comment has been removed by the author.

  6. Awesome post, Travis! That was such an amazing day with Grant, making his varnish. The neighbours were quite concerned indeed. Maybe if I were one of them I would have been too: the fumes...the location...the precautions. It did not help we both looked like the scruffiest in our oldest clothes, bent over a tripod on the parking lot asphalt. I had to throw my clothes out at the end of the day for fear of causing a fire in my landlady's laundry machine, nor did I want to alert the airline security to the little jar of proverbial liquid gold I went home with a few days later by having these stinky clothes in my suitcase! It is absolutely amazing varnish!