I had always understood that Atkin torrifed the spruce on their guitars. Here is an
article from 2015 that refers to the process as torrefaction, including this quote from Alistair Atkin:
Quote:
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"Torrefying the top really does help with stability," Alister states. "It brings the moisture content right down so when the guitar goes to somewhere like Canada in the winter, it's much more stable. It also plays a part in giving the guitar that vintage tone, crystallising the resins, which happens naturally over time.
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My understanding is that torrefaction of wood for guitars has evolved over the last decade or so. When the process first became popular, the wood was often torrefied in a manner similar to other industries, but builders found the wood to be too brittle. Over time, builders figured out that the wood needed to be dried at lower temperatures and/or for shorter periods. I attended a “luthiers’ coffee chat” at the Fretboard Summit a couple of summers ago in which Dana Bourgeios discussed the evolution of torrefaction of the woods they use (including the fact that they no longer torrefy wood in-house).