What are shingle granules?
Granules are fine-grain opaque, crushed rock that has been colored by a ceramic coating. The best granules are consistent in size, have a highly stable coloration and do not allow light to pass through them. Although the best granule colors will not fade, they will appear to change color over time. This occurs for several reasons. First, granules are delivered to the factory with a light, protective oil coating. The oil coating is applied to reduce dusting in the factory and to promote adhesion between the granules and the asphalt. One side effect of the oil is that it acts to make colors richer and darker, just like oil polish on wood furniture or wax polish on car finishes. But this oil rapidly weathers off. The loss of the oil coating changes the reflective characteristics of the granules on the shingle and may be perceived as a slight change in color. Color shifts are also caused by gradual dirt buildup, which mutes or dulls the color.
