On Jan 15, 11:22*am, Pete Snell wrote:
...
* *Opaque means nothing will pass. ...
* *Pete

Translucent might have been a better choice of word. The infrared
spectrophotometer I ran for a summer research grant only detected
radiation that passed straight through the sample, ignoring any that
was reflected, refracted or re-emitted in other directions. I
accounted for those with careful sample preparation and calibration
runs.

Absorption and reradiation at the same wavelength aren't the same as
reflection or scattering but the end result is similar, like the
diffuse light on an overcast day.

A classic optical experiment that depends on translucent material is
the measurement of relative light intensity with black paper
sandwiched between two blocks of paraffin wax. You set it between the
standard and unknown sources and slide it until both blocks appear
equally bright from the side. Then measure the distances to the
sources and use the inverse square law to calculate the ratio of their
intensities.

jsw