Which factor is NOT considered when grading marble?

When grading marble, several factors are taken into account to assess its quality and suitability for various applications. Thickness is not typically considered a grading factor because it can vary depending on the specific needs of a project rather than the inherent quality of the marble itself.

Color variation is crucial as it affects the aesthetic appeal and can determine how well it fits with design schemes. Natural veining is also significant since it contributes to the unique appearance of the marble and can indicate the geological conditions under which the stone was formed, influencing its desirability. Characteristics in fabrication, such as how well the marble can be cut, polished, or finished, also play a vital role in grading as they impact the performance and durability of the material in practical use.

Therefore, while thickness is important for practical purposes, it does not influence the grading of marble, which focuses on the material's visual and physical attributes.