I figured this out. 1. The Feather tool under Filters --> ABCs. 2. The excellent description under #6 on this post: http://inkscape-forum.andreas-s.net/topic/84362 3. I think the ideal solution would be something like what's described here http://wiki.inkscape.org/wiki/index.php/User_talk:Davidhewit...

When I center a small object on top of a large object, I want to have the smaller object mostly opaque, but to have just its edges fade off to being transparent, to make a smooth transition between them. A radial gradient transparency effect blurs more than just the edges and doesn't conform to the ...