Yes I think that will work, but might need a bit of contrast boost. My approach, FWIW, would be to begin with a canvas filled with black/white noize. Then apply radial blur with a low spin setting, maybe 15. Then, to keep hitting CTRL-F until the circular bands seem smoothed out enough - Not being concerned about contrast at this point, just to get a nice set of concentric bands. Applying the same filter repeatedly at a low setting lets you decide when you've got what you want interactively. Once I'd got a base that I was happy with, I would start to worry about contrast and start using levels, curves, or brightness/contrast to get the variance I'd like. The contrast between light and dark in the image will have a bearing both on the texture and the bump map of course and you might use different maps for each, derived from the same source image, but with differing contrast. Hope you get the effect you're seeking :)