Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Why Cannot Steel be See through?
Name: N/A
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: N/A

Here is one that I have been trying to explain for some time but have be unable to find a satisfactory answer: What makes something transparent? I understand about the index of refraction, however, it seems me that if a substance such as silicon can be made into transparent glass, and a substance like petroleum can be made into transparent plastic, and so on, it stands to reason that something like steel could be made transparent as well. Why cannot aluminum be ma transparent, ala Scotty in Star Trek IV?

The main reason is the electrons. The electrons in a metal, which give it its electrical conductivity, cause the light to be reflected. Aluminum oxide can be transparent, aluminum can not.

Yup. Glass is not pure silicon, it is silicon di-oxide (a combination of silicon with oxygen). Plastic not the same material as crude oil - they have totally changed the chemical composition and carbon is notorious for being able to do wonderfully different things in different molecules - Aluminum and other elements just do not have that ability. But, so far we have explored only a very limited range of possible combinations of elements - there are undoubtedly wonderful materials that could be made in the future. Just think - there are 92 different elements (that are relatively stable) so the number of materials with equal parts of just 2 elements is 92^2 = 8464, and you can try arbitrary combinations of any of them. The total number even of things in equal combinations would be 2^92 which is an immensely large number. And then preparation technique etc all enters in. This is why the whole field of materials science is so important these days.

Arthur Smith

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory