Thermo Treatment - a method developed in Finland for ageing tonewood

Thermo treatment - vintage vibe or voodoo?

Quality of tonewood means everything to me, because it essentially dictates whether a guitar has the potential – the genes – to become a great musical instrument. Thermo treatment is not a magic trick – it doesn’t change bad wood into good. But it is the best possible method to make sure my selected tonewood is all game to begin the transformation into a great guitar.

In this article I share with you what I know of thermo treatment of wood. It is a technology developed in Finland originally for construction and furniture industry in the 1980’s –  developed further and adapted into musical instrument wood in the 1990’s – and eventually becoming popular in other parts of the world, too. These days thermo treated wood has many nicknames: torrefied, roasted, baked or caramelized wood being the most common trade name variations recently taken into use, as thermo treatment has finally gained success also in North America.

I’m not perhaps the best expert on historic tidbits of thermo treatment development, but this is the short version as I’ve learned it from my teacher Rauno Nieminen, one of the original developers of thermo treatment method for musical instrument wood. There was this Fire Chief, Osmo Savolainen, of a little town in Finland, who knew a lot about fire. He also knew a lot about what water does to fire. And he knew what fire does to wood. It is the classic story of creative / inventive spirit: “I wonder what would happen, if I connect this and that natural phenomenon…”.

Osmo came up with an idea to treat wood with heat to make it more resistant against decaying, mold and fungus. His original target was to create an environmentally friendly, non-poisonous material for children’s outdoor playground toys.

So he placed wood planks into a container (a scary piece of equipment, that first thermo treatment facility!), which was heated up to a temperature that would normally set the wood on fire. Osmo, however, injected water vapor to the container, raising the relative humidity up to 100%, and preventing the wood from igniting. The basic idea could be compared to steam boiling. Or Finnish sauna…

Osmo’s idea worked. The wood didn’t burn – instead it came out different from what it had been before the treatment – and according to Osmo’s experiments, he had indeed reached his goal and developed a viable substitute for poisonous, impregnated wood. He presented the invention to an organisation called VTT (Valtion Teknillinen Tutkimuskeskus – Technical Research Centre of Finland) – who got interested and started its own research to find out more about what happens in the process. Don’t ask me how exactly it happened, but at the end of the day VTT went on to patent the new groundbreaking technology to its own name, dropping Osmo out of the game. The big guy ate the small guy. Sad, and unfortunately not the first (or the last) time shit happened. As I’m writing this article (middle of the night, November 28, 2016) all thermo treated wood (both in Europe and North America) that ever was or is commercially available so far, is based on this technology patented by VTT – technology that was meant to produce environmentally friendly substitute for impregnated wood for outdoor use.

But that’s not the end of it – story continues. Finnish people are often stubborn, and so was Osmo – somewhere down the road, after the disappointing theft of his original invention, he happened to tell Rauno Nieminen, the head of guitar making school in Finland, about his findings. Osmo showed Rauno an electronic microscope image of thermo treated spruce – and for Rauno, this rang a bell. He remembered seeing something very similar in Strad magazine – an electronic microscope scan of 17th century violin top… So Osmo and Rauno conjured up a special project to map out whether thermo treatment could be something useful for musical instrument wood. It started in 1996, involved the Ikaalinen College of Arts and Design (Lutherie Dept.), Suomen Ekopuu (Osmo’s company), Tampere University of Technology and a bunch of musical instrument makers – guitars, violins, church organs and more.

The project went on for years, changing format and funding channels. I hopped in to the project in 1999. Each company sent materials to be thermo treated, and every piece of wood went through a complex test routine before and after the treatment – microscopic cell structure study, sound velocity testing, bend-strength, absorption capacity measurements, workability tests, and experimental (subjective) tap tone tests by the musical instrument makers. Then each of us made musical instruments using the thermo treated materials – and slowly, through all the testing, the big picture started to crystallize.

There was indeed something beneficial to this process, that had along the study developed into new direction, as compared to the older, patented technology by VTT. Osmo, Rauno and the other researchers had realized that the treatment temperatures must be much lower than they were originally set in order the wood to become ideal tonewood. The project came to its end by the turn of millennium, and the official 75-page report was eventually published in 2002. It was a heavy duty research with tons of data. But – all this knowledge remained sort of a secret among the Finnish musical instrument makers that had participated in the project. Why so? Not because we chose to keep it to ourselves. Not because there would be a patent – there isn’t a patent for this specific method that differs from the VTT patent. It’s just that the study was published only in Finnish language! And to make things even more challenging – it was never published in digital format, not even in Finnish language!

So there I was, a young guitar maker, preparing for my first international guitar trade fair held in Frankfurt in year 2000. I had this amazing invention – thermo treated wood – in my hands. I was the first guy entering the international market with electric guitars made of thermo treated wood. I was so excited. And I was such a hopeless rookie. I was giving flyers to all visitors – and I talked and talked and talked… I learned that year at Frankfurt Musikmesse the hard way, that men in white coats showing scientific evidence just can not convince the guitar buyers. Oh well – I have worked hard since then to educate and convince players, one by one, about this breakthrough technology – and eventually things have worked out fine, as our customers have noticed through their own experience that there is something genuine to it.

For a long time it felt like we were the only ones pushing on with it, though. One of the turning points was in January 2006 when ToneQuest Report magazine published an article about us and thermo treatment. That article aroused a lot of discussion and interest in the North America towards the method, and I’d like to think that the article might have been even the nudge that resulted in the chain reaction that lead Music Man and eventually so many big and small companies to take thermo treated wood into their production. The fact that all of them are using the “VTT era parameters” is most likely a passing phase – eventually (after a lot more talking) the ship will turn and the “right kind” of thermo treatment will take over and become the standard technology.

So – what does thermo treatment do to wood? During the research in Finland, comparisons were made between untreated, treated and some hundreds of years old naturally aged pieces of wood. The main species involved in the study were spruce, alder, birch and maple. Some tests were done also with spanish cedar, mahogany, rosewood and ebony – but more studies would be required to say anything about those exotic species, cause mostly the samples exploded to sticks in the early tests.

Essentially – here’s what happens to wood in thermo treatment: Stability increases – ability to absorb moisture decreases – cell walls harden – resins crystallize (and partly vaporize) – stiffness increases – pores clean up – sound velocity increases – color deepens – weight drops (slightly). The treatment doesn’t change bad wood into good wood, but it does make the good stuff even better. The bottom line is this: Thermo treatment changes wood in the same way as decades of natural aging does, period. When done the right way, thermo treatment has only positive effects.

For me, it is simply a practical improvement. I’ve been enthusiastic about it, because it makes my guitars better – and in return makes my life easier. One example is how our Steam bass model came to exist. I started out as a guitar maker, and making bass guitars came into the picture much later. Ever since I started using thermo treated wood in my guitars, however, I was thinking that it would be very interesting to make basses, because of the increased rigidity thermo treatment does. Especially the neck can often be tracked down as the cause of so called “dead spots” – notes that decay much faster than the rest of the notes on the fretboard.

There are such notes in every instrument that decay a bit faster than other notes, but usually you call a note dead spot at the point when it is really challenging. Guitars can have this too, but in bass guitars the phenomenon can be much more dramatic. It is very common, for example, that the classic J and P style basses have dead spots on the fretboard. With thermo treatment, I felt that I might be able to work miracles and keep the problematic peak resonances in control better. Later on, when my first bass prototype was being tested in Germany by my friend Markus Setzer, one of his first comments was: “All the notes sustain in such way that it shouldn’t be possible in a bolt-on neck bass”. I was thrilled. I knew I was onto something extraordinary.

A lot of people keep asking me what’s the difference with the more dramatic (caramelized – torrefied – baked – roasted) treatment and the milder treatment I’ve learned through participating to this research back in the day. The difference is, that when the wood is “overdone”, the changes are not anymore the same as what natural aging does. The color changes a lot – the cells partially break – the sound velocity decreases – the wood becomes fragile and difficult to work with. The stability of “overdone” wood is excellent, but nobody really knows how the wood will mature regarding the fragility and broken cellular structure. My point in sharing this information is absolutely not to badmouth companies using baked wood. My sole intention is to share knowledge – exactly as I’ve been doing the past 20 years – so that more luthiers would gain from it. So there you have it, the truth, as I’ve learned it through my involvement in the development process of thermo treatment method for tonewood, and through my own experience from then on.

Lecture at Holy Grail

I did a lecture about thermo treated tonewood at The Holy Grail Guitar Show 2014. This recording was done privately by us, and even if the sound quality is somewhat compromised, here you go - might be interesting stuff for true thermo wood nerds. A fair warning though - it is 45 minutes of me, just talking...

Bottom line

Thermo treatment changes wood in the same way as decades of natural aging does, period. When done the right way, thermo treatment has only positive effects.
– Juha Ruokangas