I have made a few very simple Celtic knots before and used them as ornamentation on woodwork. I usually placed them in the center of a panel or on a clock face. A commission for a wedding gift to an Irish couple gave me an excuse to take on a larger and more involved Celtic knot pattern. It is used as a border on the frame of a clock.
The egg and dart design originated in ancient Greek and Roman architecture, and can be seen in a variety of woodcarvings, stone carvings, and plaster castings. It contains an alternating design of an egg shape and a dart or arrow. This classical motif can be seen in many historical architectural designs.