Question
Can anyone describe the chemical/bacterial/fungal(?) processes which create the beautiful patterns and colors found in the heartwood of sweetgum? After sawing many logs of varying sizes, I can tell you it is not just due to the size/age of the tree. A very healthy 30" diameter log in central Georgia (my location) can have little dark heart. On the other hand, a much smaller log may have more central heart and have streaks of the coloration running down from damage to the bark when the tree was less mature - for example, where a tree trimmer had taken a limb years earlier. I have cut the logs from 32" to 14" in diameter and have thousands of board feet which have been air drying for about a year. I cut the sapwood quarter-sawn to get the ripple satin effect and cut the heartwood however I can to get the most out of it. Love it!
Forum Responses
(WOODnetWORK Forum)
From contributor W:
I too live in central Georgia and there is a lot of sweetgum here! I have not sawn any to this point, focusing more on walnut, cherry, poplar, and oak. I cannot help you with your question, but I want to draw off your experience sawing sweetgum, if I may. I have heard you almost have to flip the cant with each board removed to relieve stress. I have also heard it is finicky to dry, in that it warps easily. What has your experience been?
The degree of twist which sweetgum can show during drying is amazing. A sixteen foot board can twist 90 degrees from end to end, unless properly restrained. I stickered my last stacks at 16" and that told me that 12" centers will be better. That takes a boat load of sticks!
8/4 and thicker throws less of a fit, but any pile of sweetgum needs weight on top. If you had a lot of sawing going on, one way to handle it would be to sticker stack the gum three feet high (for example), then pile three feet more of a more amicable wood stickered on top, such as pine or red oak. Any pile of all sweetgum really needs a couple thousand pounds on top of it.
I have decided to cut a lot of the sweetgum curly fries which I have already dried into short "project packs." The idea is to have a little kit of 20-30 board feet of shorts planed and ready for the hobby woodworker. This will eliminate most of the waste generated by my ignorance. The worst stuff will just get burned in the shop heater.
Sweetgum must be sticker stacked promptly. I have used borate mix on some of the wood, so that I could experiment with slower drying. The treasured red gum (or the heartwood with the dark coloration and streaking) is bad about cracking, but it seems that you just have to dry it and see what survives. My deliberate attempts to slow the drying seem to help with this cracking, but the pith area will crack no matter what. I coat the ends of my logs, as soon as they are felled. End coating on sweetgum is important. The ends do crack badly without it.
I am a studio furniture-maker, turner, sculptor, and have a Wood-Mizer. I like getting really big/old trees. Some went through storms maybe fifty years ago, when lightning blew a couple of 3-4" strips of bark off of the trees, yet they managed to heal over. Later, the bark may only be half as thick as where it was not damaged. There will usually be a pretty large jog in the sapwood/heart transition line.
I think it has some relationship to the air passing through the thin bark more easily than when it is thick. Since sweetgum can grow very fast on a favorable site, but might grow more slowly on a less favorable site, the more vigorous one could have thinner bark. I am not sure if the mineral streaks from injury or loss of limbs are the same as heart or red-gum.
In some trees like eastern red cedar and junipers, I often see that where a yellow-belly sapsucker has pecked through to the cambium, there will be a little blob of sap, which turns to thick gum, then later to a hard solid after it crystallizes. There will also be a little streak above and below the peck where the cells get permeated with this thick sap. This will end up left in the wood, then behind this dark rich streak, there is usually a white strip of sapwood that never made it into heartwood, because I think the air was more thoroughly shut out by the resin streak.
Yet on the same species, it is not uncommon to find older trees that are dead on one side, with a living strip growing on the other. Under this circumstance, the air travels around the edge of the living wood, through the dead bare wood, and this then turns each year's growth to heartwood the same year that it grows, without there being any sapwood under the bark near that edge.
