About a comparison between different sorts of
stones for sundial carving, sundials of Brittany
in the west part of France are pretty
instructive. The region is rich with granite and
slate, and hundreds of dials are currently known.
The oldest sundials, dating back to the middle of
16th century, are mostly carved on granite and
very few on slate. But from the very end of 16th
century on, carvers and dialists have totally
given up granite for slate. First because of the
bad resistance of granite to weathering. The few
remaining granite sundials look "erased" and
almost illegible, and they are vertical dials not
horizontal. And next because of the possibility
of easily cutting plates with any desired shape,
and of easy and very fine and beautiful carving
: some slate dials are really masterpieces. You
don't need special or heavy tools to carve slate
(or at least most of the varieties). Slate
resists much better to weathering, because, I
think, of its layer structure; for instance
don't forget that frost has no effect on slate
(in french it is said to be "ingélif" but I don't
know the english word for it). Existing dials,
even from 16th century, can be read as if they
have been carved last year. It is always amazing
to discover on a 1580 slate dial the slight lines
(less than 1 mm deep !) the dialist had drawn on
the plate to fix the place of the hours line,
digits or decoration before beginning to carve.
Granit lasts long but slate lasts even longer.
Another point. It is a spread , but quite false,
opinion that contrast of shadow on a slate plate
is low. It is quite the opposite : the shadow of
a style is very well visible, it is always darker
than slate surface that is never very dark but
more or less gray. The 500 or so slate dials
still remaining in Brittany (and in north-east of
France also) are living instances of this easy
reading.
Regards
Jean-Paul Cornec
22300 LANNION
FRANCE
48°44'24" N - 3°27'26"W
