If that is typical sweet gum spalting I can believe the little piece I turned could be gum. (BTW, I learned something from researching this: several of the references say that the sap wood of Liquidambar styraciflua is often referred to as sweet gum and the heartwood is called red gum.)
Do you have a reliable procedure for spalting on purpose? I've been doing some "recently" by the method of laying the log on the ground, kicking leaves and dirt over it, and pouring on some water when the weather was really dry (such as around here most of the last year). I've tried just setting one end of a short round directly on the dirt but it leaves the other end unspalted. Maybe turn it over every few months? This past year I've added spalted maple, dogwood, and holly to my drying racks.
If you spalt wood on purpose how do you have a secret way to know when it is "ready"? Do you use the guess, cut, and "rats, not yet" method that I use?
The holly spalted with broad areas and streaks of indistinct discoloration instead of the fine, high-contrast black lines I see in maple, birch, and dogwood. The spalted hackberry I have also has black lines but less distinct. If what you show is typical, sweet gum is different from anything else I've seen. Feel free to ship a pallet of this to me, it won't bother me at all. :-)
JKJ