a furnace for fining molten glass is provided in which glass flows in a substantially vertical direction prior to exiting the furnace . as it flows vertically , the glass is allowed to cool . this cooling , in turn , allows the glass to be removed from the furnace through a narrow passageway without producing excessive wear of the passageway . preferably , vertical flow of the molten glass at the exit end of the furnace is produced across the furnace &# 39 ; s full width . in this way , the molten glass does not stagnate within the furnace and undesirable scums on the top surface of the glass are avoided . in certain preferred embodiments , the vertical flow is achieved by a trough which has sloped sides and which connects with and extends downward from the bottom surface of the furnace .