The shoulder-stones of the ephod were not to be carved roughly. The Targum Pseudo-Jonathan on Exodus 28:11 insists the engraver work as the engraving of a ring — every letter distinct, deep enough to leave an imprint if pressed into wax. Each of the two gems carried six tribal names. Each letter had to survive a lifetime of Aaron's movements without blurring.
The Sages lingered on the craft. A signet ring is a legal object. When a king presses his ring into clay, the document becomes binding. By asking the artificer to use signet technique, the verse implies that the tribal names on Aaron's shoulders were not decoration but a living seal. Whenever Aaron moved, the twelve tribes moved with him into the sanctuary, their names leaving impressions on the air before God.
There is a lesson here about representation. A leader whose people sit on his shoulders as an engraved seal carries a responsibility no ordinary garment demands. The gems must be clear because the tribes they name are owed clarity — no blurred identities, no forgotten houses.