Luster Comparison
Three
Lustrous Material Panels, 36" x 36"
These three panels are the same size, same design, even
same size squares. They serve to illustrate the differences
between three lustrous surfaces; lustrous concrete (here
terracotta-colored concrete), brushed metal (blue brushed
aluminum), and wood veneers (Etimoe, or African Rosewood).
One can see three bright diagonal areas angling upward to
the left in both the Etimoe on the right and the blue
aluminum in the center. When I did the concrete, I did the
exact same layout for the mold, forgetting that the inside
mold surface is reversed. The result is that the three
bright diagonal areas angle upward to the right.
Most materials have surfaces which are non-lustrous. Light
which strikes the surface is scattered, or redirected, away
in more or less a uniform 180 degree spread. This is
technically an isotropic
(uniform) light
redistribution. Lustrous materials have a surface condition
which causes light to be redirected more strongly in one
direction than others, and is anisotropic,
or non-uniform.
The panels above serve to illustrate refractive and
reflective luster. The wood
has surface cells
that are semi-transparent, looking like tea-colored glass
under a microscope. Light enters from one direction, and
can only emerge from the cells according to principles
governed by the index of refraction, like a camera lens.
Because the cells are not all uniform, curving somewhat as
they grow, the lens effect is somewhat inexact, and the
luster areas are relatively wide.
The brushed
aluminum has
a surface that was sanded (brushed) in one direction to
give a uniform surface, which in reality is a series of
linear scratches. For purposes of this discussion they may
be considered a multiplicity of very long, very shallow
mirrors. For this reason the luster area is very confined,
the brightness quite intense in the squares in the middle
of the light bands and quickly falling off at any distance
from those squares.
The lustrous
concrete is
an example of a lustrous opaque material. This may be a new
type of luster, differing from both the mirror effect of
the metal and the refraction of the wood cells. It is
caused by articulating the surface in a series of ridges
and grooves at particular angular relationships with each
other. The luster from this technique (patent pending) is
broader and softer than either the metal or the wood.
