9

1720 Chapter 16: Material Editor, Materials, and Maps
has an i ndex of refraction (IOR) of 1.5, while the
alcohol in the glass has an IOR of about 1.3. To
create a physically accurate model of this situation,
use three glass materials: one for the glass itself,
one for the alcohol, and a third material for the
surfaces where they touch each other. For this
third material, set the “inside” IOR to 1.3, and the
outside IOR to 1.5.
Inter face
Light Persi stence—In conjunction with the
Persistence Distance, controls the percentage of
lightthatthevolumetransmits.Forexample,if
the color is set to R=G=B=0.5 and the Pers istence
Distance is set to 2.0, then objects with a thickness
of 2.0 units will appear 50 per cent t ransparent.
Default=white (R=G=B=1.0).
Because transparency depends on the thickness of
the object, objects with varying thickness show
different transparenc y depending on the angle
from which they are viewed.
Index Of Refraction—Specifies the Index Of
Refraction (IOR). In the physical world, the IOR
results from the relative speeds of light through
thetransparentmaterialandthemediumtheeye
orthecameraisin.Typicallythisisrelatedtothe
object’s density. The higher the IOR, the denser
the object. Default=1.5.
See Extended Parameters Rollout (Standard
Material) (page 2–1471) for a list of IOR values for
commonly encoun tered materials.
Outside Light Persistence—In conjunction with the
Persistence Distance, controls the percentage of
light trans mitted on the other side of a sur face.
When set to the default of black, this control has
no effect. See the sec tion “Adjacent Refractive
Materials,” above. Default=black (R=G=B=0.0).
Index Of Refraction (out)—Sets the IOR on the other
side of a surface. When set to the default of zero,
this cont rol has no effect. See the section “Adjacent
Refractive Materials,” above. Default=0.0.
Persistence Distance—In conjunction with the
Light Persistence color, controls the percentage of
light that the volume transmits. It is the distance
at which light transmission is reduced to the
percentage specified by the Light Persistence RGB
values. Default=1.0.
If you specify an Outside Light Persistence color,
that setting also uses the Persistence Distance.
Ignore Normals—When on, the renderer does
not use normals to decide whether a light ray
is entering or leaving the object. Normally, the
shader uses normals to decide whether a ray is
entering or leaving an object. (I t is entering if the
normal points toward the ray, leaving if the norma l
points away from the ray.) This can present a
problem for rendering objects whose normals
are not unified. When Ignore Normals is on, the
shader decides whether a ray is entering or leaving
the object by counting the number of times the ray
has intersected the object. Default=off.
Opaque Alpha—When on, refracted rays that touch
the environment don’t generate a transparent
alpha value. (This is how 3ds Max usually treats
the environment.) When off, refracted rays that
touch the environment render a transparent
alpha value, which can help if you plan to use t he
renderingaspartofacomposite.Default=off.