Scott Leavengood of Oregon State University was kind enough to pull together this list of resources for those of you interested in learning more about wood hardness.

ASTM Standard D143, 2009, "Standard Test Methods for Small Clear Specimens of Timber," ASTM International, West Conshohocken, PA, 2009, www.astm.org. 31 p.

ASTM Standard E10, 2012, "Standard Test Method for Brinell Hardness of Metallic Materials," ASTM International, West Conshohocken, PA, 2012, www.astm.org. 32 p.

ASTM Standard D7136, 2012. "Standard Test Method for Measuring the Damage Resistance of a Fiber-Reinforced Polymer Matrix Composite to a Drop-Weight Impact Event," ASTM International, West Conshohocken, PA, 2012, www.astm.org. 16 p.

Bektas, I., M.H. Alma, and N. As. 2001. Determination of the relationships between Brinell and Janka hardness of eastern beech (Fagus orientalis Lipsky). Forest Products Journal 51(11/12):84-88.

Forest Products Laboratory. 1999, "Wood Handbook-Wood as an Engineering Material," Gen. Tech. Rep. FPL-GTR-113. Madison, WI: USDA, Forest Service, Forest Products Laboratory. 463 p.

Niemiec, S., G.R. Ahrens, S. Willits, and D.E. Hibbs. 1995. Hardwoods of the Pacific Northwest, Research Contribution 8. Forest Research Laboratory, Oregon State University.

And more casual but interesting stories and looks at Janka:

http://piemonte.di.unito.it/Atomi/JANKA.ASP.html

Article from Makezine.com: How Wood Hardness is Measured

Elizabeth Baldwin has over 20 years of international wood sourcing experience. Very widely traveled, her résumé's "Special Skills" section includes "the ability to eat anything from raw horse to deep-fried scorpion." She serves as Metropolitan Hardwood Flooring's (metrofloors.com) ECO (Environmental Compliance Officer) and deals daily with the "green alphabet soup" of today's industry: FSC, CARB, LEED, and much more. She blogs for Hardwood Floors on all things green (and, as she says, " 'grey' and 'blue' and almost every color except 'black and white.' Nothing in this world is black and white, particularly not 'green issues.'")