Glass used in sculpting can be:

When considering the processes involved in glass sculpting, the correct answer highlights the versatility of glass as a medium. Glass can indeed be cast in molds, where molten glass is poured into a molded shape to create a solid object. This method allows for intricate forms and details to be captured. Additionally, glass can be heated to a malleable state and blown, a traditional technique that enables the creation of various shapes and sizes by using a blowpipe. This dual capability—casting and blowing—illustrates the range of techniques available in glass sculpting, allowing artists to explore different artistic expressions.

The other options do not accurately reflect the properties and techniques associated with glass sculpting. For instance, the assertion that glass can only be molded at room temperature disregards the fact that glass must be heated to a specific temperature to become workable. Claiming that glass can only be used for flat surfaces overlooks the three-dimensional possibilities that sculpting offers. Lastly, the idea that glass is fashioned exclusively by hand tools ignores the role of various techniques, including machinery and processes such as blowing and casting, that expand the artist's capacity to manipulate glass.