More clarification of my last post -- sweet gum (Liquidambar
styraciflua) and red gum (Eucalyptus camaldulensis), as shown here
by their scientific names, are two different genera.  My guitar builder
friend has samples of both.  The heartwood of the sweet gum is olive
green to greenish brown color while the red gum varies from a rust to
amber color (exactly the color of Ampico blocks).

The sapwoods of both abruptly change to a pale tan or cream color.
Other then that, the hardness and grain characteristics appear to be
the same, with the sweet gum grain slightly tighter.

Brian Thornton - Short Mountain Music Works
Woodbury, Tennessee
http://www.shortmountainmusic.com/

 [ At http://en.wikipedia.org/wiki/Red_gum : "Red Gum may refer to
 [ any of a number of species of Eucalyptus or the closely related
 [ Corymbia, including ..."  Redgum eucalyptus is described at
 [ http://www.hort.purdue.edu/newcrop/duke_energy/Eucalyptus_camaldulensis.html