Very cool. You can also adjust out the most of the gray to get more of a gesso white on white relief effect by pushing the contrast or whatever adjusters you have access to. But this has a neat effect as you've used it.
If you don't have photoshop or what have you you can post the BW image you used and I can adjust it for you and re-post it for you to grab and use to see the difference to get just the relief effect.
Go Rondo! Push that envelope.
"Not a bit is wasted and the best is yet to come. . ." -- remembered from a dream