What does 'slumping' in glass manufacture refer to?

Slumping in glass manufacturing refers to the process of heating glass until it becomes soft enough to take the shape of a mold. During slumping, the glass is placed into a mold that determines its final shape, and as the temperature increases, the glass starts to soften and flow. This method allows for intricate shapes and designs to be created, enhancing the aesthetics of the final product.

The process generally occurs at a temperature that is below the melting point of the glass, enabling it to become pliable rather than fully molten. This characteristic of slumping is essential for creating three-dimensional objects from flat sheets of glass, such as bowls or art pieces.

The other options describe different processes or aspects of glass manufacture that are not related to slumping. For instance, cooling glass rapidly refers to the annealing process, adding color to glass involves incorporating colorants during the melting stage, and breaking glass into small pieces does not relate at all to the shaping or molding process.