To get green, you add iron to the sand mixture, causing the entire color spectrum to be absorbed by the glass, but green.
(you; add; iron; to the sand mixture) Context(you add,List([14, 21))):(you; add iron causing; the entire color spectrum to be absorbed by the glass) Context(you add causing,List([14, 55))):(the entire color spectrum; to be absorbed; by the glass)
you add,List([14, 21)) you add causing,List([14, 55))
you you the entire color spectrum
add add iron causing to be absorbed
iron to the sand mixture
the entire color spectrum to be absorbed by the glass
by the glass