A short interesting article on the iconography of St. Lawrence:
The earliest portrait of the saint that I have actually seen is a 5th-century fresco that portrays him as a youthful man, tonsured and wearing the dalmatic of a deacon. The youth, the tonsure, and the dalmatic will stay with him through sixteen more centuries of religious art, with only a few exceptions (example without a dalmatic, example with lush hair). Sometimes the saint will also be pictured with a maniple, a length of cloth that was worn over the left forearm by deacons and priests at Mass, as in the first picture at right. In one case that I have seen, the artist managed to sneak in a bit of the "stole," another vestment that deacons wear at Mass underneath the dalmatic.3
The fresco painter apparently did not include a gridiron. Some of the plaster has fallen away at the bottom, so we cannot be sure. But by the 6th century, the saint is strongly associated with the gridiron, as in the first image at left. In the ensuing centuries, it is by far his most common attribute (example). In most portraits it is shown in a diminutive size as a mere attribute, and in one painting it is reduced to just a grid pattern on the dais beneath Lawrence's throne.
In the Golden Legend the executioners also apply red-hot pitchforks to Lawrence's body, so this becomes another attribute, sometimes used instead of the gridiron (second picture at right).
Another attribute is based on two of the miracles ascribed to St. Lawrence. One involved a heavy golden chalice that the emperor Henry II had given to the Church of St. Lawrence in Eichstätt. When Henry died and his misdeeds were piled up on one side of the scale, the devils hoped to gain his soul. But then St. Lawrence put the chalice on the other side, and Henry was safe. In anger, one of the devils broke off a piece of the chalice, which he referred to as a bowl. In the other miracle a deacon in St. Lawrence's church in Milan dropped a crystal chalice. It broke into pieces, but upon the deacon's prayers St. Lawrence reasssembled it as good as new. Owing to these legends, in some images the saint holds a chalice-like bowl, sometimes with a broken-off piece, as in the third image on the right. Another influence on the chalice attribute is Augustine's remark that St. Lawrence served the church in Rome and "it was there that he administered the sacred chalice of Christ's blood; there that he shed his own blood for the name of Christ."
