Firebricks found in limekilns are usually used as a lining and are therefore not an integral part of the structure. Finding a particular named-brick doesn't necessarily date the site. It only provides a possible date that the brick itself may have arrived on the scene. Knowing when a brickyard started using a name might be helpful, but the age of the structure could be older than the brick if the brick was brought in at a later date to line an existing structure. Conversely, finding an old brick at a site does not preclude the possibility that a brick was imported at an earlier time, before the kiln was built, and reused subsequently at the time the lining was last installed.
Bricks come in all different shapes, sizes, and colors.
Shapes vary from cylindrical, square and triangular, to the rectangular ones we see most frequently. Sizes vary as shrinkage of the clay, while it is burning in a brick kiln, is difficult to control. Also, originally there were no standards for size, but common building brick tended to be smaller than firebrick. Firebrick is seldom, if ever, red like common building brick. Iron in the clay turns these brick red when they are burned in the brick kiln.