Here is what Furch say..
'BLUE SW guitars feature a solid-wood construction that combines Sitka spruce and black walnut. They have a fine attractive appearance and produce a musical sound with pleasing mids and transparent highs.
The soundboard of BLUE SW models is made from high-grade Sitka spruce. The back and sides feature high-quality black walnut. Open-Pore Finish leaves wood pores exposed, which preserves the natural acoustic properties of tonewoods. This combination of high-quality solid tonewoods and proprietary finishes produces a beautiful musical sound across the entire tonal range, with balanced midrange frequencies.
The premium nature of Furch BLUE SW guitars is underscored by the fact that the soundboard is tuned using the voicing process, which enhances the guitar's tonal properties to the highest level. Thanks to that, Furch BLUE SW guitars have a crystalline clear, harmonically rich, balanced, and highly dynamic sound across the entire tonal spectrum.
Furch BLUE SW guitars feature Open-Pore Finish, a special thin finish that promotes the natural sonic qualities of tonewoods and provides an excellent level of surface protection. The finish accentuates low frequencies and produces a natural woody sound.'