• Traditionally, a mosaic is a picture or pattern produced by arranging together small colored pieces of hard material, such as stone, tile, or glass.
• Mosaics have a long history, starting in Mesopotamia in the 3rd millennium BC. They have been used by virtually every culture and religion to decorate buildings
• The direction in which tile is laid is called the opus, and there are no strict rules, as each artist develops their own style.
•  The visual flow created by the opus pattern is referred to as the andamento.
• There are several main opus styles used by mosaic artists: opus regulatum (tile, or tesserae, are laid in a grid) opus tesselatum (visualize a brick wall), opus vermiculatum (the tesserae are cut to imitate the shape of the image in ever widening lines), opus classicum, which combines tesselatum with vericulatum, opus palladianum ( a random design also called crazy paving), and opus sectile, (larger pieces are cut to describe a form). This style looks more like stained glass art.
• I create both indoor and outdoor mosaic art. Typically my outdoor mosaics are in the form of a stepping stone. The art is created in my studio and attached to a cement stepping stone in one unit after the whole design is completed. This is called the indirect method. The direct method is attaching tesserae directly to a base, one piece at a time
• This example is a combination of opus regulatum and opus sectile. It is a stepping stone for outdoor use.
  

Here is an example of opus regulatum. The tile are laid out in a specific geometric pattern.