Jamieson, Fausset and Brown on Exodus 28:15-29

15-29. thou shalt make the breastplate of judgment with cunning work--a very splendid and richly embroidered piece of brocade, a span square, and doubled, to enable it the better to bear the weight of the precious stones in it. There were twelve different stones, containing each the name of a tribe, and arranged in four rows, three in each. The Israelites had acquired a knowledge of the lapidary's art in Egypt, and the amount of their skill in cutting, polishing, and setting precious stones, may be judged of by the diamond forming one of the engraved ornaments on this breastplate. A ring was attached to each corner, through which the golden chains were passed to fasten this brilliant piece of jewelry at the top and bottom tightly on the breast of the ephod.