[Maxakarudy]

Judging from what I've seen & been shown..

"Blocking" is heavey stretching against a soild object, like a wooden stump or steel block, the metal is thinned out at the point of contact between the hammer head & the material that the metal was resting against, like planishing on a dolly.

"Hollowing" is different, the use of a hollow stump or sandbag is what the metal is rested on, the hammer head forces the metal to stretch into an unsupported void, this also causes tucks to be formed aswell.