a "hot top", also known as a "", is a specialized riser, used to help counteract the formation of pipes when casting ingots. it is essentially a live open riser, with a hot ceramic liner instead of just the mold materials. it is inserted into the top of the ingot mould near the end of the pour, and the rest of the metal is then poured. its purpose is to maintain a reservoir of molten metal, which drains down to fill the pipe as the casting cools. the hot top was invented by robert forester mushet who named it a "dozzle". with a hot top only 1 to 2% of the ingot is waste, prior to its use, up to 25% of the ingot was wasted.