Even when the simple mat was replaced by more permanent stone altars at the beginning of the Old Kingdom, the altar often had the offering hieroglyph carved on the top, or was made in the form of the offering sign. The upper surfaces of the tables were often carved with images of loaves, trussed ducks, and libation or other vessels required. *These images would then serve as magical substitutes for the real food offerings, backed-up by the offering formula and lists of specific offerings.*
http://www.touregypt.net/featurestories/offering.htm

Ptolemaic Altar
This Ptolemaic altar has images of loaves, trussed ducks, and vessels. These would serve as magical substitutes for real food offerings.
http://www.eternalegypt.org

Το "υλικές" ως εκ περισσού, για το "reality".