Mike, compression fractures, frets or crysals(all the same) will appear as small cracks across the grain on the belly of wood bows. Generally where the limb bends the most.

The ones I was talking about don't run across the grain, but lengthwise with the grain. I get those sometimes from adding heat to a bow blank and so far they haven't caused any problems for me. The future may decide different, but I haven't noticed any ill effects from them and they don't seem to be getting any larger the more I shoot the bow.
Like I said before they don't show up till you stain the bow, otherwise you can't even see them. They are like little hair line squiggles all up and down the belly, never seen them on the back or ring side of any of my bows, at least not yet knock on wood!  

I just made a longbow from ironwood. After putting the last coat on and trying to decide which limb would be my top and bottom limb for my floppy arrow rest placement. I notice a squiggly line going across the grain on the fade about where the fade meets the limb. If it was a compression crack should I have noticed it when I put the first coat of tung oil on and not the 7th? Could it be in the finish? Will it hurt to shoot it? or can it be fixed easily?   Thanks Mike

Chrysals that are localized to one spot are caused by a bad tiller. That is the limb is bending too much in that place. I always fixed them by retillering. Leave that area alone and remove wood from above and below. Retiller the outer limb. If you cut out the chrysals and do  not retiller won't they come back? I've also fixed these by gluing on some rawhide over them. If the chrysals are over the entire limb then the fault is in the design? Jawge