Define the following terminologies used to describe mosaic compositions: tesserae, interstices, and tonal variation.

- Tesserae: Small pieces of glass, stone, ceramic, or other materials used to create a mosaic design. These pieces are typically arranged and adhered to a surface to form a pattern or image.

- Interstices: The spaces or gaps between tesserae in a mosaic composition. These spaces can vary in size and shape, and can be left empty or filled with grout or other materials to create contrast and definition within the design.

- Tonal variation: The variation in color, shade, or intensity of the tesserae used in a mosaic composition. Tonal variation can add depth, dimension, and visual interest to a mosaic design, creating a sense of movement and texture within the overall artwork.

Tesserae:
- Small, flat pieces of material used to create a mosaic.
- Can be made from a variety of materials, including stone, glass, ceramic, or metal.
- Vary in shape, size, and color.

Interstices:
- The spaces between the tesserae in a mosaic.
- Can be filled with grout, mortar, or other materials.
- Can be left empty to create a negative space effect.

Tonal Variation:
- The variation in lightness, darkness, or color of the tesserae within a mosaic.
- Creates a sense of depth, texture, and realism.
- Can be achieved through the use of different colored tesserae or by varying the size and shape of the tesserae.