The True Color of Slate

By Cass Jacoby.  

Slate is multi-colorful roofing material that you can use to create a truly unique roof. Here is what color designations mean when it comes to slate. 

When you think of slate, odds are you are thinking of some kind of grey. Unless you are a geologist, you probably don’t think of slate color in terms of its chemical and mineral composition. So you don’t immediately think of the chlorite that creates green slate, the hematite purples or the iron oxide reds of slate. Natural slate is so much more than greys and blacks, it truly covers the color spectrum. 

While descriptions of slate colors vary from supplier to supplier, generally North American roofing slate falls under general color descriptions of black, gray/black, gray, green, gray/green, purple, variegated purple, mottled purple/green, and red.  

The subtle variation of color, shade, veining and grain on each slate shingle on a roof is a unique aesthetic advantage of slate. The wide variety of natural slate colors available offers limitless opportunities to create unique roofs. Here is everything you need to know about slate colors according to the National Slate Association to embrace the aesthetic of roofing slate on your home. 

Slate color designations 

In the roofing industry, there are two color adjectives usually applied to roofing slate: weathering and fading. According to the National Slate Association, slate can be known as “weathering” and “non-weathering”, or “fading” and “non-fading,” however, in most cases, and in current usage, the terms “unfading” and “non-weathering” or “fading” and “weathering” are often used interchangeably.  

This color weathering (or absence of color weathering) produces either the “weathering” or “unfading” designation of slates. Thus, in describing commercial roofing slate colors, you will often see the words “unfading, semi-weathering or weathering before the color. These terms merely signify the color stability from slate from any given source. 

Fading/weathering slate 

Fading or weathering is used to describe slates that would show various percentages of color change slowly as they are exposed to the elements. Fading describes slate that, once exposed to the elements, notably lightens in color because of their mineral makeup. Sometimes this color change can denote a deterioration of deleterious minerals that can mean a shorter life expectancy of these slates. Often, these are terms that largely characterize color changes more than anything else.  

Color weathering happens due to the calcite and iron compounds in the slate. These minerals are not deleterious and don’t affect the life expectancy of the material. The percent of color change can vary from quarry to quarry and is dependent on the mineralogy of the stone, which is why terms like semi-weathering may be applied to highlight how the slate will weather. 

Unfading/non-weathering slate 

Unfading slates more or less maintain their original color on the roof. However, even for unfading slates, color change on a roof can take place as the result of environmental pollutants, (like high sulfur content in acid rain hitting the roof). 

Conclusion 

Slate roofs are beautiful because they embrace the serendipity of nature. You can lay a single color on your roof or a custom combination of various colors — whatever suits your fancy. In fact, it is a common practice to blend various colors of slates, with both unfading and semi-weathering characteristics, to create a truly unique custom roof. 

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About Cass  

Cass works as a reporter/writer for RoofersCoffeeShop, AskARoofer and MetalCoffeeShop. When she isn’t writing about roofs, she is putting her Master degree to work writing about movies and dancing with her plants.