Copal incense an aromatic tree resin was known to the Aztecs as food for the gods. The sacred "copalli" (in the original Nahuatl language) was considered "blood" of trees and was burned atop the Aztec pyramids as an offering to the deities.
Copal incense also served as an integral part of ceremonies designed to bring good harvests. The ceremonies consisted of dripping sacrificial blood on copal that is then used to cense seed maize before planting.
Divination ceremonies also used copal incense. Patterns in the smoke were interpreted by a shaman who cast fourteen grains of corn through the smoke onto a cloth. The shaman would then interpret meaning based on the patterns the corn produced as it was cast through the smoke and where the corn grains fall.
The proper method to burn copal is to place sand in a purified vessel. Burning coals are then placed atop the sand and the appropriate deities are politely "invited" to partake in the feast. Only then can copal be placed on the burning coals.