Piercing. The process of perforating, punching or cutting out open areas in fully struck metal items as part of their intended design; openwork. Piercing is the most severe design element a coin or medal designer can employ in creating a design, it removes the opportunity for any design, texture, patina finish – anything! – in that area for both sides.

By creating "vacant space" or "negative mass" the designer consciously permits of any surface held behind the item; it also gives the greatest possible emphasis to the edge that has been outlined. Thus the outline shape of a pierced item often becomes more important than the design shown on either side. Such openwork adds exclusiveness to certain medallic designs, as with decorations of honor or orders, most of which have openwork and those of highest rank have the greatest amount of piercing and for the greatest visual distinction for pierced coins. Piercing is a technique for struck medals only, as cast medals have openwork created by the casting form.

If it is not practical to construct expensive piercing tooling, as for extremely short runs of simple pierced designs, medallic items may be drilled and cut out by hand with a jigsaw (also called coping or jeweler's saw). This work is performed at a bench often by a chaser or as part of the chasing work.

Production run piercing is accomplished with a piercing tool on a punch press. Special tooling is prepared for each openwork design, consisting of four parts: (1) a in which holes are cut to allow scrap to fall through, (2) of hardened steel, cut with the exact design to be cut out, mounted on a base plate, (3) a to position the piece to be pierced, mounted to the die, and (4) a made with projections of hardened steel (generally made of drill rod), and fastened to the upper part of the punch press.

The special tooling is constructed by a tool and diemaker to exacting specifications. The piercing must match perfectly the shape of the item and not cut into the design of either side.

The piercing punch is positioned (setup) in a punch press; its action can be described as follows: the item is placed in the nest fitting snugly into position, the press is actuated, forcing the piercing punch with its projections against the fully struck up medallic item of softened metal (lying next to the punching die), thus driving the projections through the item and the die, and punching out the piercing scrap which falls through the base plate.

Such piercing action, much like trimming, creates a burr on the side where the punch exists. This burr is removed by chasing or by abrasive blasting.

Very elaborate piercing designs infrequently call for multiple piercing when the open areas are so close together there is inadequate room for all tooling. This requires, therefore, two – or more – sets of piercing tooling, with a separate press run for piercing accomplished by each set of tooling.