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Slate Terms

Unfading Slate

An unfading slate does not change color when exposed to weather or sunlight (Examples, LaBana, Buckingham, Grayson, North Country and Vermont Unfading Green).

Semi-Weathering Slate

Slate is made up of many minerals. Chlorite, for example, gives some slate its green color. On exposure to sunlight and weather the color transforms to a rich pallet of peach, salmon and tan. Strata and Grey-Black slate similarly transform to buffs and tans. These slate are described as semi-weathering.


Secca slate has dominant and secondary planes of compression, due to upheaval of the rock structure during its formation, but the grain on the surface has no particular direction, due to competing secondary planes of compression. It is split on the dominant plane and the surface has a ‘fish-scale’, shimmering appearance (the secondary plane).


Hebra slate has a uniform plane of compression, producing a relatively smooth face.


These are concentrated areas of a specific mineral. Pyrites are common, of different types. Some give unusual deep green blotches, other ferrous pyrites giving ‘rust spots’. Mica and silicates produce a ‘glitter’ in the slate surface.

Graduated Roof

These slate roofs begin on the eave with the thickest and largest slate. As the roof progresses up towards the ridge, the slate become narrower and shorter, emphasizing the height of the roof. The example given is the lakeside mansion of slate baron Jack Williams.

Variegated Roof

A variegated roof mixes different colors of slate to create a roof design. This example is a mix of unfading and semi-weathering Vermont Green.

Intermingled Thickness Roof

This style of roofing incorporates slate of different thicknesses throughout the roof. The effect is to give a textured appearance, especially effective when the slate used is otherwise very similar.

Graduated and Variegated with Intermingled  Thickness

These roofs may have the same size and type of slate but with varying thickness, giving a textured look to the roof. This example is variegated with a staggered butt in addition!

Chapman Slate

Chapman or Lehigh Valley slate came from Pennsylvania in the early 20th century. Once a popular slate in the Mid-Atlantic, these still endure, as does their beauty.

Buckingham Roofs

These roofs are going to last forever. Note how the roof forms such a large proportion of the front elevation of the house.

Baltimore Turrets

This outstanding turret is built in Peach Bottom slate as are the adjoining roofs, where the slate are cut to form octagonal patterns. 

Typically built on every block corner, this is another Peach Bottom turret.

This 25th St landmark was once the crown jewel of the neighborhood. A ten-sided apron in Unfading Vermont Green sweeps to a Greco design made with Peach Bottom and Unfading Vermont Red. Here it merges into a dome, capped with decorative metal work. This one is ready for restoration.

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