Abstract: This specification is directed to a dam structure which may be used in a float glass chamber for separating a hot entry end of the chamber from a cold exit end of the chamber. The dam has been specially designed so that it will mix tin currents sheared from a glass ribbon moving thereover of higher temperature with colder tin moving around the edges of the dam and returning from downstream of the float chamber. The mixing of the tin currents occurs at a position spaced outwardly fromm the position of movement of the glass ribbon over the dam so that glass ribbon is not subjected to zones of tin having varying temperatures which could cause optical distortions therein.