RE: isenglas
I'll take a stab at this and know that someone will correct me or expand on
this if I'm wrong or incomplete.  When I was growing up, isenglas was the
name given to the material in the windows in stoves and furnaces and other
areas that required the ability to see something through.  Made of mica and
very brittle but highly heat resistant and translucent, almost transparent
sometimes.  That name was also used, I think inaccurately, to apply to any
non-glass transparent material like the soft windows in convertibles. Later
the generic term plastic would replace that kind of use, just as later
generic use of the word Plexiglas applied to any transparent plastic
material that came along after Plexiglas.
This is my recollection of the use of the term.  And I haven't heard anyone
refer to 'isenglas' for many years.
Footnote
Just did a search, found this under alternate spellings in Wikipedia
*Isinglass should not be confused with Eisenglass which is made from sheets
of mica and was once commonly used as a heat-resistant substitute for
glass<http://en.wikipedia.org/wiki/Glass>
.*:
* *