Thermally Aged Tonewood - a way to make great guitars even better

Thermally Aged Tonewood

Tonewood quality means everything to me, because it essentially dictates whether a guitar has the potential – the genes – to become a great musical instrument. Thermally Aged Tonewood is not a magic trick – the thermal ageing process doesn’t change bad wood into good. But it is the best possible way to make sure my tonewood is all game to begin the transformation into a great guitar.

In this article I share with you what I know of thermally aged tonewood. The process was developed in Finland originally for construction and furniture industry in the early 1990’s – developed further and adapted into musical instrument wood in the 1990’s – eventually becoming popular in the rest of the world, too. These days thermally aged tonewood has many nicknames: torrefied, roasted, baked or caramelized wood being the most common trade name variations recently taken into use, as thermally aged tonewood has finally gained success also in North America.

I’m not perhaps the best expert on historic tidbits of thermally aged tonewood development, but this is the short version as I’ve learned it from my teacher Rauno Nieminen, one of the original developers of thermally aged tonewood. 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, Osmo placed wooden 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 picture. The big guy ate the small guy! Sad… and unfortunately not the first (or the last) time either. As I’m writing this article (middle of the night, November 28, 2016) all thermally aged tonewood (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 chemically impregnated wood in outdoor applications.

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 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 this thermal treatment against wood decay and fungus could be something useful for tonewood. It started in 1996, involved the Ikaalinen College of Arts and Design (Lutherie Dept.), Suomen Ekopuu (Osmo’s company), Tampere Technical University, professor Pertti Nieminen in the lead, 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 thermally 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 never was and still isn’t a patent for thermally aged tonewood – a method that differs significantly from the VTT patent. No… 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 – Thermally Aged Tonewood – in my hands. I was the first guy entering the international market with electric guitars made of thermally aged tonewood. 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 thermally aged tonewood. That article aroused a lot of discussion and interest in the North America towards the method, and I’d like to think that this very article might have been even the nudge that resulted later in the chain reaction that lead Music Man and eventually so many big and small companies to adapt thermally aged tonewood 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 thermally aged tonewood will take over and become the standard technology.

So – what does thermal ageing do to tonewood? 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 tonewood in the thermal ageing process: Stability increases – ability to absorb moisture decreases – cell walls harden – resins crystallize (and partly vapourize) – rigidity increases – pores clean up – sound velocity increases – colour deepens – weight drops. The process doesn’t change bad wood into good wood, but it does make the good stuff even better. The bottom line is this: Thermal ageing changes wood in the same way as decades of natural ageing does, period.

For me, it is simply a practical improvement. I’ve been enthusiastic about it, because it makes my guitars better – and in return, it 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 thermally aged tonewood in my guitars, however, I was thinking that it would be very interesting to make basses, because of the increased rigidity thermal ageing 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 thermally aged tonewood, 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 ageing process I’ve become familiar with through participating to that research back in the day. Well, the difference is, that when the wood is “overly baked”, the changes are not anymore the same as what natural ageing 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 some 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 thermally aged tonewood, and through my own experience from then on.

Lecture at Holy Grail

I did a lecture about thermally aged 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 aged tonewood nerds. A fair warning though - it is 45 minutes of me, talking, talking...

Bottom line

Thermally Aged Tonewood is identical with wood that has been seasoned for decades. When done the right way, the thermal ageing process has only positive effects to the wood.
– Juha Ruokangas