Ive seen roofs with brown or rusty-brown slate. Where does brown slate come from?
Brown slate is not brown when first quarried. Brown slate occurs in “weathering” or “semi-weathering” veins and after exposure to the elements. Which slates are destined to turn brown and which are not is not readily apparent (it takes a few months of sun and rain), so if brown is not a desired color in the finished roof, then “unfading” slate should be specified. The percentage of brown that will occur in “weathering” and “semi-weathering” slate will vary from quarry to quarry with some deposits turning almost 100% brown and others as little as 10%. Knowing the weathering characteristics of the stone you’re using makes good sense and avoids unpleasant surprises and misunderstandings. In addition to natural forms of weathering, slate can be discolored by any number of environmental factors including tree sap, rusty roof metal and airborne pollutants.
