A common misconception associated with the nomenclature
of describing slate is the fact that frequently
the terms weathering and fading are erroneously
interchanged. Slates are classified as fading or
unfading solely according to color permanence. Fading
is characterized by a chalk-ashen residue that lessens
the slates aesthetic beauty. The term unfading often
refers to Blue-Black and Blue-Gray slates.
The term weathering refers to colored slates. While
colored slates do not fade, some will experience
some color change. The weathering of slate is induced
by the oxidation of minerals as they are exposed
to the elements. The weathering process slowly changes
the color of the individual slate. Weathering slates
will often exhibit changes that result in the color
gradually turning to buff, brown, grays, or tan
Colored slates can be classified as one of three
types. The classification is based upon the extent
to which the slates molt. The term weathering refers
to slates that will exhibit the largest number of
individual pieces that will transform from the original
color to an earth tone. Slates deemed non-weathering
would exhibit the least amount of color change.
As the name would imply, semi-weathering slates
are a combination of the two aforementioned types.
Some of these slates will exhibit color change while
others remain their original shade. The percentage
of semi weathering slates that will experience color
change is variable depending upon the location in
the quarry from which the slate is extracted.
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