A bunch of heat treated fir strips - a couple untreated for comparison
Heat treating of wood is old. Who hasn´t scorched a piece of wood on the campfire and ssen it darken. It is also well known that wood treated like this was more rot resistant than untreated, but also that it lost some strength. It becomes brittle.
The last decades there has been research going on in Scandinavia and elsewhere on industrially heat treated wood. Oxygen free oven heating to approx 200° C for many hours. All species are treatable. The color darkens according to temperature. Moisture content decreases as does resins. It becomes more rot resistant and dimensionally more stable, and it gets lighter and more brittle. Heat treated fir looks and feel a bit like Western Red Cedar with its advantages and disadvantages. The color is more yellowish though.
Mats Nording in Hudiksvall sent a bunch of fir boards to the "sauna" and ripped them to kayak strips. Next step is to transform them to a Black Pearl.
I look forward to follow the process. Mats will take photos and report from the building process.
A couple of links (in Swedish):
Info from Luleå Institute of Technology (more links in the paper)
Report from LTU (Luleå Institute of Technology) – industrial design
Heatwood – commercial applikations