ToneQuest Report / Thermo Treatment



“The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs. There´s also a negative side.”
– Hunter S. Thompson

Perhaps you are aware that a dark underbelly also exists in the guitar and gear business, where competitive envy turns ugly, creative ideas are stolen for profit, where the weak are squashed by the strong, and gangs of knuckle-draggin’ guitar evangelists troll the information highway for converts and disciples to feed their bitter, bloated egos. Curiously, you don’t always find quite the same seedy, carnival midway atmospheric in many other enthusiast groups.

Photographers, for example, can surf countless web sites and forums like for meticulously detailed, unbiased camera reviews and discussion pages rich with sage advice from working pros. You rarely hear about camera manufacturers suing each other over single cutaway designs or read Internet posts by department heads of major manufacturers accusing small, custom accessory builders of selling “snake oil”. In fact, camera manufacturers often share technology for their mutual benefit. The same can be said for enthusiast-driven industries like cycling, skiing, vintage car restoration, hunting, fishing, homebrewing and cooking. But jump on a guitar-oriented forum and all too often it seems that the “bitch and whine” contingent are out in full force, doing what they do best – bitching and whining. So we were less than surprised when we were directed to a web forum “discussion” of our interview with Juha Ruokangas and review of two Ruokangas guitars in the August 2005 issue of TQR, where we found more bitching and whining, with one idiot even claiming that we had been paid to write our review. Well, of course we were paid – in gold Double Eagles no less. Isn’t everybody? And it wasn’t long before we received the following comments from a well-known New York guitar builder:

“I was excited when I got the new issue of ToneQuest and saw The Mythology of Tone subject. I was looking forward to a good discussion. Instead, what we got was a puff piece on Ruokangas Guitars with a bunch of voodoo about “ThermoTreatment” for drying wood. This was about as enlightening as the violin guy 20 years ago who boiled his spruce with shrimp shells to duplicate the “secret” of Stradivari! There was also the Mike Tobias/Steve Rabe Vintage Shaker Table in the ‘80s that was supposed to accelerate instrument aging by putting guitars on a Shaker table and exposing them to computer generated sound waves. The list goes on and on… Where is the inquisitive question to Ruokangas of “What does ThermoTreatment consist of?” or “Do you have any empirical evidence that it makes a difference?” He refers a couple of times to “researched facts” or “studied facts” – but where is the data?”

tqr_2006_1Our well-known guitar builder poses a fair question, and one we deliberately chose not to address in the original interview and “puff piece” review for two reasons:

While a credible claim for the effectiveness of Thermo-treating wood can (and will) be made, we felt that the sheer quality, detail, tone and workmanship of Ruokangas’ guitars deserved to be described without placing undue emphasis on the perceived benefits of Thermo Treatment. Thermo-treated or not, our point was, they are extraordinary guitars, yet we were clearly incapable of assigning a precise value to the role that Thermo Treatment ultimately plays in their overall sound. To do that would have required two “identical” instruments – one Thermo-treated and one not – and even then it’s doubtful that the thermo-controversy would have been satisfactorily doused, since no one in America has a clue what thermo-treatment really is (hence, it must be bullshit).

Second, as of today, buying an instrument built with thermo-treated wood is an option only in Finland, where the process is patented. What was the point? Like cheap Mexican Dilaudid and Porfidio Barrique 100ml, if you want some of this, you’ll have to hit the road, Jack, ‘cause for now, you can’t get it here.

Our well-known New York guitar builder also referenced the Shaker table and computer-generated soundwave “voodoo” once developed by the now defunct Timber Technologies Co. Perhaps you’ll recall a reference to the same company made by Joe Perry’s guitar tech, Jim Survis, in the March 2002 issue of TQR:

TQR: Did you feel that his (Jimmy Page’s) ’59 Les Paul was really special when you were working with it?

“Sure… it was very spanky and bright. It has a lot of miles on it, and instruments always sound better when they have been played a lot in front of the amps, soaking up all of the reverberation from them. In fact, we used to take Jimmy’s guitars, including the ’59, and while he was tracking other rhythm tracks we would place the guitars on stands right in front of the speaker cabinets to absorb the sound coming off of them. There was actually a company out in California called Timber Technologies that had this military-grade sound generator that they would clamp your guitar in and bombard it with sound waves for three days for a fee of $100. I told Joe Perry about Jimmy leaving his guitars in front of the speaker cabinets, so we sent a Custom Shop Mary Kay Strat that Joe had gotten from Fender to Timber Technologies. The guy said, “Look, send it to me, and if you don’t like it, don’t pay me. We got it back, and it was awesome. The thing rang like a banjo, and acoustically, you’d hit the strings and it would go brrrnnggg. It was dramatically different. I’m not even sure if that company is still around.”

tqr_2006_2The point is, chillun… When you’re chasing tone and inspiration, who are you going to believe? At what point does an “innovation” become useless “voodoo?” Do Bill Callaham’s tremolo blocks really make a difference? Are TonePros hardware, Evidence Audio cables and NOS tubes “snake oil” too? It’s easy enough to read the technical specs found in a detailed camera review and choose your next digital SLR with absolute confidence, but do you choose replacement pickups, speakers, effects, amps, or a guitar based solely on published specifications and technical data? Evaluating guitar tone shouldn’t be confused with the rigorous study design required for clinical pharmaceutical trials – afterall, good, better, or bad tone won’t kill you. When it comes to discovering inspiring guitars, amps and tones, there seems to be little benefit in keeping a closed mind in the absence of “compelling data,” but we’re going to give you some anyway.

We’ll stick by our original claim that Ruokangas builds exceptional, extraordinary guitars that double as remarkable works of art. As for the “researched” benefits of Thermo-treated wood, let’s cut to the source, beginning with Juha Ruokangas, who provided the following responses to our questions via laptop as he nursed a beer by the fire from his home in Finland… Kippis!

TQR: How and when did thermo-treatment of wood begin, and who participated in the study of thermo-treated wood for musical instruments?

Thermo Treatment is a patented Finnish invention. The patents are owned by VTT Technical Research Centre of Finland, and the process has been in use since 1990 by industrial wood technologies in Finland. Thermo Treatment for musical instrument woods has been studied by Tampere Technical University in close co-operation with several musical instrument manufacturers in our country. The official research started in 1996. This study led to a 75-page report (published in 2002), which includes lots of laboratory measurements of various wood species before and after thermal treatment. We were one of those musical instrument manufacturers who participated in the study by sending wood to be treated and experimenting with the result. Each body, neck and fretboard plank we sent was measured for weight, moisture content, cell structure, stiffness, etc., before and after the process. For us, the first years were experimentation for fun, and then, even to our own surprise, we started really understanding that there is something beneficial to this process.

The co-operative parties in this study were:

Ikaalinen College of Arts and Design (Lutherie Dept.)
Suomen Ekopuu (the company responsible for the thermal treatment)
Tampere University of Technology
National Technology Agency of Finland (financier of the project,
Lottonen Guitars (steel-stringed acoustic guitars, archtops,
Taisto Pietilä (violinmaker)
Soitinrakentajat Amf (kanteles, guitars,
Kanteleverstas Koistinen (kanteles,
Landola Guitars (steel-string acoustics
Ruokangas Guitars (electric guitars,
Liikanen Musical Instruments (classical and flamenco guitars,
Porthan Church Organs
Virtanen Church Organs

tqr_2006_3Each company used thermo-treated materials to build instruments that were then compared to the same kind of instruments made of non-treated materials. The manufacturers have, at the very least, compared tap tones, workability, how finishes work on the treated surfaces, weights, colors, and the tone of the finished instruments.

TQR: What did you observe in the instruments you built with thermo-treated wood in regard to appearance, the way the wood worked in the shop, and tone?

Thermo-treated wood acts differently when planed, sanded, etc. It feels very dry and the dust smells different – old and sort of “smoked.” It’s difficult to explain verbally. The wood is also tanned in color throughout. For example, maple appears yellowish/brown without any artificial coloring. Another apparent change is the bending strength (stiffness) of the wood. When we clamp two identical neck planks on the side of a table (the neck hangs out from the edge) and place weight on the tip of the plank, the wood naturally bends down a bit. Thermo treatment takes some flexibility out of the wood structure (the cell walls harden/crystallize/age) and the plank bends less than the non-treated piece. The exactly same thing occurs when wood has been air-dried for 50-100 years. Also, I think the increased stiffness improves the tonal behavior of a guitar, since it makes the neck resonate less, making dead spots less obvious or even disappear. Tonally, the differences are even more difficult to describe in detail. For example, the tap tone of a spruce top for a jazz guitar definitely changes when thermo-treated. Some of those cool lower mids jump out in a way they didn’t before the treatment. Many professional musicians have described that the guitars “sound vintage.” I know all this may sound like voodoo, but perhaps when you’ve read more about the process itself, you’ll understand that there’s a logical and acceptable explanation to these changes. Believe me, I was very skeptical, too, during the the first few years. I’m someone who wants to stand behind his words 100%.

Here is a practical example about the stability issue… A small amount of Arctic Birch was thermo-treated in 1998. From that batch, I’ve had a 6mm thick Arctic Birch flat top (cap) for an electric guitar laying around the workshop for years. It’s a bookmatched plank, sanded to thickness. So this particular piece of Arctic Birch has been on the shelf and on the worktable here and there over the years, and it has remained perfectly flat. If I had a similar piece of maple or non-treated birch, rest assured, it wouldn’t have remained flat through all the seasonal changes in Finland. I mean, even though the wood is kept in a warm place, the air humidity changes drastically indoors because of the heating here in wintertime.

TQR: Can you describe the thermo-treated procedure used for the wood in your guitars?

tqr_2006_4I can’t go into the smallest details, because even I don’t know them. The patent holder and the licensee company who treats the wood for us keep the details to themselves. One thing to point out is that the patent itself was published prior to the Tampere University study we’re describing. So, the actual patent is more general and not the exact tonewood procedure, which was developed later and is done only by one company in Finland. I’ll describe what I do know… The wood is placed in a container, which is heated, and the air moisture content is very high to prevent the wood from burning. Actually, the system might be called a kind of “steam heating” procedure. I don’t know exactly how long the tonewood is subjected to heat, but I do know that the temperature and amount of moisture change during the process is very precise. One thing that happens is that all organic “junk” in the wood vaporizes, crystallizes, or comes out of the wood pores with the heat/steam. The pattern of the process is computer controlled, parameters change from one wood species to another and by the thickness of the wood to be treated. When the wood comes out of the container it can’t be worked right away, because the moisture content is close to zero %, so it’s actually under the balanced humidity level of normal air moisture content. We have to wait 3-4 weeks until the wood reaches a more balanced humidity level. When it reaches that, the wood is very stable and good to work with.

TQR: Have you noted improved stability of thermo-treated necks?

From a builder’s point of view, the improved stability is the best feature of the whole process. Thermo-treated maple is very stable. Naturally, it still has to be straight-grained – thermo-treatment doesn’t change bad material to good! It simply is a far better method to dry wood than the conventional machine-drying. It’s so close to natural seasoning and aging that it is very difficult to notice any differences between the two, except that the color of the wood doesn’t change in naturally aged wood as it does with thermo-treatment.

TQR: What types of wood benefit most from thermo-treatment?

We have thermo-treated maple, alder, arctic birch, spruce, rosewood, ebony and spanish cedar. Maple, alder, arctic birch and spruce benefit from the treatment. The others we’ve tried – and as you see they all are more or less tropical woods (rosewood, ebony and Spanish cedar) would need to be experimented with much more before I can say anything final. So far, there have been severe problems with cracks in the tropical woods, so we don’t offer them thermo-treated at all for now.

TQR: How were direct comparisons made between wood that was naturally aged and thermo-treated?

Through microscopic cell structure study, sound velocity testing, bend-strength, absorption capacity measurements, workability tests, and experimental tap tone tests by normal spruce manufacturers (by subjective evaluation, naturally…)

tqr_2006_5One thing worth mentioning is that church organ builders have started to use thermally-treated wood in Finland during the last ten years, also for stability reasons. They have learned from experience that they have less warranty issues when the wooden constructions are made of thermo-treated wood. I don’t think they’ve thought about the tone that much – more just to pay a bit extra for the treatment to improve the general quality of their product.

Thermo-treatment was primarily developed to make wood more stable in industrial use, and it is used quite extensively by other kinds of wood industries in Finland for wood floors, solid wood furniture manufacturing, construction wood and so on. Each of these industries is very large, and they profit by the wood being more stable. They don’t have to care about the tone of wood, naturally, but these companies would never use thermo-treated wood if there wasn’t some genuine profit in it – fewer warranty issues and so on. So, there are several big thermo-treatment facilities in Finland today providing more stable wood. The tonewood treatment is just a small side path, and is done only by one company that specializes in it. And – since we’re really a tiny little country in the middle of nowhere (if I may say so), it’s only natural that most people in the USA don’t necessarily know of thermo treatment yet. Nevertheless, the benefits are real, they have been thoroughly researched and documented, and they are commonly understood and accepted here in Finland.

The following is an abstract of the full study of Thermo-treated wood submitted by Professor Pertti Nieminen, et al.

by Pertti Nieminen, Taisto Pietilä, Pekka Suhonen Tampere University of Technology, Finland Laboratory of Engineering Geology

The aim of this study was to determine and verify factors affecting the most important properties (i.e.sound, durability and appearance) of wooden musical instruments and to follow the behavior of the completed instruments in a chamber where different weather conditions were simulated, as well as determining the correlation between thermal treat- ment and natural aging of the wood. Remarkable changes in the cell tissue were observed after thermal treatment. The heat seemed to cause a type of melting or crystallization phenomena on the wood surface. Also, hydrophility decreased considerably during the tests, which can be seen as a decrease of the balancing moisture. When inspecting the pore size distributions of different tree species before and after thermal treatment, one could observe an increase in the amount of the large (>1 micrometer) absorption pores and, respectively, a distinctive decrease among the small (<1 micrometer) water pores. Another change in the structure of the cell tissue of the coniferous tree is connected to the behavior of the so-called “ring-like” pores. Dried spruce, for example, has a surface structure where ring-like pores have been closed in connection with drying. Thermal treatment, however, will break these pores open. When comparing the surface structure of thermo-treated spruce with spruce dried naturally for one hundred years, a clear structural similarity can be observed, with a similar stiffness and velocity of sound attained. When measuring the sound velocities, thermal treatment seemed to have a significant influence on the attained level of the sound velocity. In low temperatures, (<200 C-grades), the velocity increases from 0-1000 meters/second. In temperatures too high for thermal treatment for musical instrument wood, (i.e. clearly more than 200 C-grades) the sound velocity begins to decrease respectively. Furthermore, the attained level of the sound velocity is dependent upon the density and initial moisture of the wood.

The results shown in this research are to be taken as guidelines. For example, the following features have been observed: When thermally treating tonewood, the length of the process and temperature play a significant role in the success of the method. It is important to take into consideration the differences between wood species. It was also observed that the inner factors, such as density and moisture content, affect the changes achieved through thermo-treatment.

tqr_2006_6It was clearly observed that the treatment temperature affects the achieved sound velocity of wood samples. Treatment in too low a temperature only dries the wood like conventional machine drying, producing no benefit for tonewood. For example, the sound velocity or weight of the wood does not change. Respectively, too high temperatures leave the tonewood fragile, making workability worse. In the correct temperature, however, there are several benefits: the wood stabilizes (ability to adsorb moisture decreases), stiffness increases, the weight drops, sound velocity increases, the wood color deepens, and the wood resonates better (partially because of the increased sound velocity).

Thermal treatment of broad-leaved (deciduous) and conifer trees differ from each other. Deciduous species such as alder or birch can be treated in higher temperatures to make them work very well as tonewoods. Higher temperatures change the structure of the conifer species (spruce, pine) to the extent that they do not work well for building musical instruments. Milder treatment maintains the natural elasticity of the conifer wood and the desired elements of good quality tonewood improve in the manner of natural aging of wood. The research results correlate well with the experience of the musical instrument makers co-operating in this study. The correlation between measured values and experimental data is significant when comparing the original qualities of the wood samples (growth speed, what season the tree was cut down, etc.) with the treated samples – sound velocity compared to tap tones and workability…

Through measurements and experimentally-built musical instruments, this research results in the conclusion that when thermally treating tonewoods in a specific manner observed, the changes in wood are the same as in naturally aged wood, whereas certain qualities of wood improve while the wood maintains its workability and strength. Further, the benefits of thermo-treatment seem more apparent among the higher quality wood species treated.

ISBN 952-15-0971-6
ISSN 1238-075X

Our sincere thanks to Juha Ruokangas and Professor Pertti Nieminen for providing English language transcripts of the abstract and conclusions.

Pertti Nieminen, Professor, Ph.D.
Tampere, Finland

So, is thermo-treatment really some kind of dark “voodoo” brewed in Finland by sunlight-deprived trolls with entirely too much time on their hands, or is it a truly important innovation of significant value in guitar construction? When we published an overview of the Plek machine with Joe Glaser in the January 2003 issue of TQR, we heard shouts of “snake oil!” too, yet the Gibson Custom Shop is now installing a Plek machine to dress the frets and cut the nuts in every guitar they build. Remember this – ignorance is fed by the fear and resentment of things not understood, and there will always be “experts” who refuse to believe that anything worth knowing could possibly have escaped their attention (because in their minds, they have nothing left to learn). And on that score, they will always be right.

Should Thermo-treatment become available in the United States (and we believe it will), you’ll hear about it first, right here.


ToneQuest Report, January 2006