Francisco de Zubrarán
St. Lawrence
1636
Oil on canvas
The Hermitage, St. Petersburg, Russia
Wearing a red dalmatic and
maniple,
a band of cloth that was worn over the left forearm by priests and deacons at Mass
the saint holds the gridiron that was the instrument of his martyrdom. Lorite Cruz (184) suggests that his dalmatic is red because that is the liturgical color for the feast days of martyrs. That is, on those days the priest's outer vestment is a red chasuble and the deacon's a red dalmatic.
Embroidered on the dalmatic is an image of a bearded saint sitting on a throne with a sword, probably St. Paul.
Read more about images of St. Lawrence.
Source: this page at Wikimedia Commons.