Assertion: reflecting telescope's mirror | /r/HasProperty | completed by the end of 1981
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Source sentences:
text: The mirror was completed by the end of 1981; it was washed using 2,400 US gallons (9,100 L) of hot, deionized water and then received a reflective coating of 65 nm-thick aluminum and a protective coating of 25 nm-thick magnesium fluoride.