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I found this wood on the side of the road. It was big, thick, and heavy, so naturally I took it home. When I cross-cut it, I noticed this star-like pattern. It's throughout the wood and seems to be around the edge of the heart wood.

It looks too straight to be wood rot. What is this?

Crosscut wood with dark patches

Scribblemacher
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  • Looks like spalting -- staining due to the tree having a fungus infection. That can produce interesting color patterns on the faces of boards, if you're lucky. It's pretty much harmless unless there is real rot, and even that can be stabilized. – keshlam Oct 08 '16 at 05:15
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    I'd vote wet wood and sap over spalt, but hard to say at a distance. – Aloysius Defenestrate Oct 08 '16 at 14:23
  • Good point, AD. – keshlam Oct 08 '16 at 22:23
  • That looks like classic water staining to me. The end grain is like a sponge so it can soak water deeply which is why the stains run so deep. – Graphus Oct 09 '16 at 08:40
  • If you put that as an answer with a bit more information about it, I'll accept it. Is this a temporary condition? Does it cause any problems working with it? I did find it on a day where there had been rain in the morning, but that was several weeks before I cut into it. – Scribblemacher Oct 09 '16 at 14:33

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As requested I'm turning my Comment into an Answer.

These look like classic water stains to me. The end grain of wood is likened to the open ends of a bundle of straws and can absorb moisture like a sponge which is why stains can run so deep.

Note that if the staining runs very deeply indeed say 4" (10cm) or more, or clearly progressing down through the longitudinal grain (which isn't absorbent) it is from fungal activity.

Is this a temporary condition?

The colour change is usually permanent (as in it won't go away on its own or fade from sunlight exposure).

It is possibly treatable with certain kinds of wood bleach though. If the stains are due to iron in the water good results should be achieved using oxalic acid which is the classic treatment for this type of staining:

Oxalic acid for dark water stains

Source: Repair a Water-Damaged Finish on Popular Woodworking.

Does it cause any problems working with it?

If it's just staining the wood won't be any different that you'd notice. With many woods however if water is in contact with it for a long time (either in one go or through repeated wetting cycles) decay can set in, but staining will often occur a long time before decay starts.

It's hard to tell for sure from the photo but the wood looks sound so this could merely be a cosmetic issue. If not the soft earlywood (the pale parts of the grain) will be softer than normal, noticeably spongy or 'punky'.

Graphus
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  • Thanks for all the extra details--this was a fantastic answer. I've done a few cuts into the wood and haven't noticed any sponginess. In fact, it's the opposite--whatever this is is very dense and hard, and barely responds to sandpaper. – Scribblemacher Oct 12 '16 at 12:58
  • @Scribblemacher Thanks! Hard to ID wood definitively from photos (and sometimes in the flesh LOL) but that could be fir, which is usually noticeably tougher and stronger than pine. But there are many types of pine and they vary quite a bit from species to species. If it is pine it might be older growth (closer ring spacing = slower growing). The more of the dark latewood that a piece of softwood has the heavier it will be, and also harder and stronger. – Graphus Oct 13 '16 at 06:59