They mounted the onyx stones in gold filigree settings, engraved like a seal with the names of the sons of Israel.

Exodus 28:9
Take two onyx stones and engrave on them the names of the sons of Israel:

Exodus 28:11
Engrave the names of the sons of Israel on the two stones the way a gem cutter engraves a seal. Then mount the stones in gold filigree settings.

Exodus 28:12
Fasten both stones on the shoulder pieces of the ephod as memorial stones for the sons of Israel. Aaron is to bear their names on his two shoulders as a memorial before the LORD.

Exodus 39:5
And the skillfully woven waistband of the ephod was of one piece with the ephod, of the same workmanship--with gold, with blue, purple, and scarlet yarn, and with finely spun linen, just as the LORD had commanded Moses.

And they worked onyx stones enclosed in ouches of gold, graven, as signets are graven, with the names of the children of Israel.