It is probably repousse, not reticulation. True repousse is done on a pitch bowl, and the work is raised by hammering from the back. 99% of what we see is actually stamped in a set of dies, though ( especially handles).
Reticulation is done by several methods. The method developed by Heikki Seppa is the most popular.
You use a silver alloy of 80-83% silver (coin silver) and the rest copper. The silver sheet is repeatedly heated to develop a severe case of fire scale (copper oxide), then pickled in acid to remove the copper, leaving a fine silver skin and an alloy core. This is brought to red heat and the core melts before the surface, causing the wrinkling called reticulation. It takes a deft hand, and the failure rate in learning makes water quenching 1095 look like a piece of cake.
While reticulation is stunning, it would be a real trick to do knife handles by this method. If you see a handle with a reticulated surface, it is almost surely stamped in a set of dies.
Stacy