Upon exposure to the weather, all slate is changed slightly in color. The extent of this color change varies with different slate beds, being barely perceptible in certain slates. Those slates in which color change but slightly are classed as “permanent” or “unfading”. Those in which the final result is more marked and varied are known as “weathering slates”.
Weathering is the natural result of exposure to the elements and in no way affects the durability of the stone. The weathering characteristics of the various slate types vary from quarry to quarry and must be taken into consideration to maintain some control over the final appearance.