Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods. The oldest surviving casting is a copper Mesopotamian frog from 3200 BCE. Specific techniques include lost-wax casting, plaster mould casting and sand casting. Welding is a process where different pieces of metal are fused together to create different shapes and designs. There are many different forms of welding, such as Oxy-fuel welding, Stick welding, MIG welding, and TIG welding. Oxy-fuel is probably the most common method of welding when it comes to creating steel sculptures because it is the easiest to use for shaping the steel as well as making clean and less noticeable joins of the steel. The key to Oxy-fuel welding is heating each piece of metal to be joined evenly until all are red and have a shine to them. Once that shine is on each piece, that shine will soon become a 'pool' where the metal is liquified and the welder must get the pools to join, fusing the metal. Once cooled off, the location where the pools joined are now one continuous piece of metal. Also used heavily in Oxy-fuel sculpture creation is forging. Forging is the process of heating metal to a certain point to soften it enough to be shaped into different forms. One very common example is heating the end of a steel rod and hitting the red heated tip with a hammer while on an anvil to form a point. In between hammer swings, the forger rotates the rod and gradually forms a sharpened point from the blunt end of a steel rod. Glass Glass may be used for sculpture through a wide range of working techniques, though the use of it for large works is a recent development. It can be carved, though with considerable difficulty; the Roman Lycurgus Cup is all but unique. There are various ways of moulding glass: hot casting can be done by ladling molten glass into moulds that have been created by pressing shapes into sand, carved graphite or detailed plaster/silica moulds. Kiln casting glass involves heating chunks of glass in a kiln until they are liquid and flow into a waiting mould below it in the kiln. Hot glass can also be blown and/or hot sculpted with hand tools either as a solid mass or as part of a blown object. More recent