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| There are three types of slate color: unfading, weathering and fading. |
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Unfading
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Unfading (sometimes referred to as non-weathering) slate keeps its color for the life of the stone. From decade to decade there is no obvious color change; some colors mellow slightly; some intensify. But green will remain green, gray-black will remain gray-black, red will remain red.
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Click on a photo to see a larger image, to read a description and to learn what sizes are optimal.
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| Gray/Black |
Gray/Black |
Gray/Black |
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| Green |
Gray Green |
Purple |
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Mottled Green
& Purple |
Red |
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Weathering
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| Weathering slate commonly changes color within a few weeks, months or years of installation. No two roofs weather identically, and often some shingles keep their original color while adjacent shingles turn brown or buff, producing a multi-colored effect. Slates that undergo this partial color change are sometimes called semi-weathering. Once the color has changed, as with copper that has acquired its patina, the color remains stable. Service life is undiminished. It should be noted that some in the trade invert the meanings of weathering and "fading" (below). |
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| Click on a photo to see a larger image, to read a description and to learn what sizes are optimal. |
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| Sea Green |
Gray Black |
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| Purple |
After
Weathering |
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Fading
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A third type of slate, fading, is no longer widely used east of the Mississippi river. Such slate commonly lasts 20-60 years in mild climates, considerably less than unfading or weathering slates whose service lives in harsh climates can well exceed 100 years. Fading slate is relatively common in California and in other locales where climate is forgiving and where slate is sought more for its fire resistance and design value than for its durability.
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Fading slate changes color, often beginning within a few years, because it possesses an excess of certain minerals. All slates are comprised of several minerals, including iron and calcite. Uninjurious in small amounts, too much iron rusts and too much calcite effloresces, turning the slate brown or chalky. The color change is a mark of degradation. This process is accelerated in colder climates, subject to freeze/thaw cycles, and where acid rain is prevalent. It should be noted that some in the trade invert the meanings of fading and weathering.
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Be sure that the appropriate slate is being used for your climate and for your expectation of durability.
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| © 2001 Slate International, Inc. All rights reserved. |
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