[GreenKeys] "I'm not a cop, but I play one on TV!"

[Jim Haynes]

I believe Teletype originally used cotton ribbons, because they hold
the most ink and that's what the users wanted.  I believe the nylon 
ribbons were recommended for the later machines which needed more
durable ribbons.  The Model 15 parts book shows 7835 ribbon, black.
Model 32/33 uses 181129 ribbon, but doesn't say if it is nylon or
cotton.  Then the press associations and W.U. had their own choices of
ribbons, sometimes using purple instead of black.