Ok, now look at what I did.... :p
First try, with Geninne's tutorial. Uneven lines, and smeared. :/
Second try. Own design. Still look weird and uneven stamping area. But outerline looks better this time. :p
They are actually wood carving tool. They are sharp but the carving is not precise enough. I think I need to get a proper (better) tool for rubber carving.