The Sage Polishes the Iron Mirror

From D5.11, Iskandar Tests the Sage, the Physician, and the Cup. It illustrates D5.11.10–16:

D5.11.10
He sent that iron to the learned man,Who took it in his hands, and work began.
D5.11.11
From that dark iron, polished clean and bright,He quickly made a mirror full of light.
D5.11.12
They took it to Iskandar when dark fell,And kept the secret close, and did not tell.
D5.11.13
Without a word, he left it in the wet,Until a mask of heavy rust had set.
D5.11.14
He sent it back to test the scholar’s mind,And thus prolonged the riddle he designed.
D5.11.15
The sage restored its brilliance, clean and bright,And sent it back at once, all filled with light.
D5.11.16
He treated it, so damp would not so fastBring back the darkened tarnish of the past.