How C.F. Martin and other guitar makers are using the age-old technique of torrefaction to artificially age guitar tops.
The torrefaction of wood is an ancient process that was further developed by Viking societies in what is now Scandinavia and Northern England. Typically, wood or grain stores are exposed to extreme heat in a low-oxygen setting to avoid combustion, so as to remove moisture. Not only does this process remove moisture absorbed from the outside world, it removes moisture inherent within the cell structure, permanently altering the material in cellular interiors.
Its original purpose was to increase resistance to the effects of variable humidity in the environment, greatly reducing decay in animal feed, while torrefied wood used in outdoor construction repels precipitation and resists swelling and cracking. Today, it is used on an industrial level to create wooden fuel pellets that produce heat energy in a cleaner, highly efficient manner.
Only recently was it discovered that torrefaction alters the cellular structure of the treated wood, so that it is almost identical to wood decades or even centuries old, when viewed under a microscope.
*This article was revised in November 2016*
Toasty and Tasty
The slang term of a “toasted top” is being used these days to describe torrefied spruce, because it often has patches or streaks of brown tints, not unlike a piece of toasted bread. But other than darkening the whitish spruce to a greater extent based on how long it is torrefied, the popular name is inaccurate.
Where toasting requires ventilation and constant airflow, torrefication requires the opposite to keep the wood from bursting into flame and ultimately incinerating at the ridiculously-high temperatures required to “artificially age” the wood.
C.F. Martin & Co. has quietly been looking into torrefied wood for some years now, after studying torrefication techniques in Finland, where it has been used since the Middle Ages to treat building timber. The process is 100% chemical free, which fits well into the company’s commitment to responsible environmental practices and concerns.
Finnish guitar makers like Juha Ruokangas have been experimenting with torrefaction since the mid-1990s and compiling the scientific data as to why and how it affects guitar tone.
In a press release dated January 12, 2015, Martin announced their new Vintage Tone System, or VTS. This is a proprietary form of torrefaction that micromanages the process, allowing them to zero in on an artificial age. It also allows for torrefied tops without the telltale toasty streaks. Read more about Martin’s VTS HERE.
Luthier Dana Bourgeois has been experimenting with torrefication in a more visible way longer than other American builders, as was Huss & Dalton. Gibson has been using torrefied fingerboards for some time, and Bob Taylor believes strongly that a torrefied top will guarantee fewer structural issues as a guitar ages. And given the recent high-profile success of the new Martins with torrefied tops, I expect to see it springing up in many more places sooner than later.
At first, Martin expected to use torrefication as a way to introduce a change of color into the wood, for things like fingerboards or top shading without the use of toner or dyes, so long as there was zero negative impact upon tone production. Instead, they stumbled upon a change in tone that was very much for the better.
According to Tim Teel, Martin’s Director of Instrument Design, they made an R&D test guitar, basically an HD-28 with a spruce top that had been shaded via torrefication. For Teel, the results were startling.
“I immediately noticed it had this chime to the trebles that I recognized from some of the old Martins we have from the 1920s and 30s.” he said to me, as he took out examples of spruce that was torrefied to varying degrees.
There is an old method of dating wood called the Candle Test, used to date violins. Holding a light behind wood recently harvested will show a bright round spot of glowing orangeish-yellow. Older wood, of say 100 years in age, allows much less light to show through, while wood that is 200 or 300 years old will show little or no light at all.
Why this happens remains a mystery. But it makes sense to me that the matter inside the cells or between the cell walls (cellulose and sugars, etc.) has become crystallized to the point that it refracts the light, or otherwise somehow absorbs it.
The spruce used on the first VTS Martins register on the Candle Test to be about 300 years old.
Since 2015 Martin has offered two levels of torrefication. M2 is the designation similar to their first torrefied tops, but is not being mentioned in public with any particular age associated to it.
The M1 designation has little or no noticeable color change and is being touted as targeted to approximate spruce used during Martin’s Golden Era of the early twentieth century. The tops appear slightly yellowed or off-white, compared to spruce that has had no cosmetic toner applied. This spruce is toner-free, yet it still resembles the sound board on a vintage Martin.
Originally reserved only for the Authentic Series of vintage reproduction models, M1 VTS torrefication has since appeared on several limited editions and is now available as a Custom Shop order. Check with your Martin dealer to find out which spruce species are included for custom Martins and with VTS tops.
The marketing language implies they are able to zero in on a specific decade. I recall the behind the scenes language used at the Martin factory was “80 to 100 years old” when it came to using microscope comparisons between the M1 torrefied spruce and spruce taken from actual vintage Martins.
Increased Stability and Accelerated Tone
Torrefied tops do not react to changes in relative humidity like those made with normal spruce. The spruce is less likely to swell or sink due to the time of year or how dry or wet it is outdoors. According to one Custom Shop employee the torrefied tops do not react to humidity at all.
A senior member of the Repairs department told me that the first Martin made with an experimental torrefied top was donated to a non-profit organization to auction it off. The guitar was left in a glass case under bright lights, where it dried out and cracked. The torrefied spruce allowed for a tiny crack under conditions that would have split a typical new top from bridge to end block.
But it is the way the torrefied spruce sounds that has everyone at Martin so enthusiastic.
Does it sound just like an old guitar? Well, in my opinion, I will say it sounds noticeably different and for the better compared to similar guitars made with normal tops. It makes a brand new guitar sound more alive and awake and responsive. It increases the “openness” and may also increase the high treble ring, so that a top made from Sitka spruce or European spruce acquires a chime more Adirondack spruce.
To my ear, Sitka spruce tops benefit most noticeably from the VTS treatment. But guitars made with Adirondack tops do indeed sound more opened up, with played notes encountering less resistance from the soundboard, so the tone swells effortlessly in all directions, rather than skipping along the surface of the voice like a stone across a lake – my typical metaphor when describing the sound from a brand new Adirondack spruce top.
Most of the new Martin models released for 2015 have torrefied tops, and the entire Authentic Series have been upgraded to M1 torrefied tops, braces and bridge plates.
Torrefication processes at Martin are now well established. From the get go I met no one who works there that wasn’t noticeably excited whenever it was mentioned. So I think it is safe to say you ain’t seen nothin’ yet compared to what we will be seeing down the line.
We shall also be seeing more and more torrefied wood from other guitar manufacturers. Wood charmer Dana Bourgeois has only become more enthralled with the results and potential of torrefication, and Winter NAMM 2015 revealed that Taylor’s 600 Series is now converted to torrefied Sitka spruce with maple back and sides. The damn has burst, so hang on to your hats!
And that is one man’s word on…
Torrefication of wood used for acoustic guitars