I'm not sure if anyone is still following this discussion, but I think I may have something interesting to add to it and would really appreciate any feedback.
I'm not 100% sure I'm right, but I can't see any holes in the argument.
First of all, I think the difference is as stated above:
of = constituent/material/ingredient used to make something
from = process
Here's the interesting part:
In order to support the "of=constituent" and "from=process" hypothesis, if we look at how changing verb tenses affects the meaning, the difference becomes pretty clear:
For cases with 'made from', the meaning only changes slightly. The change has to do with the point in time from which you are viewing the process.
Ex. 1: Present tense (made from)
That window is made from bullet proof glass.
[meaning: Whenever a window of that type is made, bullet proof glass is used to make it.]
Ex. 2: Past tense (made from)
That window was made from bullet proof glass.
[meaning: When that particular window was made, bullet proof glass was used
to make it.]
Ex. 3: Present tense (made of)
That window is made of bullet proof glass.
[meaning: The material used to make that window is bullet proof glass.]
Ex. 4: Past tense (made of)
That window was made of bullet proof glass.
[meaning: the window has changed state. Either 1. the window has changed structurally (most likely it was broken or had a hole or holes shot in it). This type of statement would normally be followed by something like: How did it break? How did a bullet get through it? 2. The window has undergone some kind of chemical change. In this case, the above statement means “That window is no longer made of bullet proof glass.” OR “The nature of the bullet proof glass has changed to something else, i.e. it is no longer bullet proof glass.” ]