Here is Shodai Hoan tsuba with a yakite-kusarashi (or kusarakashi -- the term is often shortened in usage) finish. The recognizable motif of a kiri-mon may be seen in the lower-left quadrant, and others appear elsewhere on the plate. I believe the effects are achieved via the process I described in my earlier post.
Florian, as far as I know, the creation of amida-yasurime was often accomplished by painstakingly careful application of the chisel onto the plate, at least in the tsuba I'm familiar seeing this presentation in (e.g. some of the Owari province artists and groups, such as Yamakichibei, Toda, Fukui). Attached is a Nidai Yamakichibei tsuba where the amida-yasurime was first chiseled into the plate, and then (perhaps?) there was some application of acid afterwards to soften the effect. This is how it appears to me, anyway.