Surah 70. Al-Ma'arij, Ayah 8

Cf. xviii. 29 (where the wrong-doer will have a drink like melted brass in Hell); and xliv. 45, (where his food will be like molten brass). Here the appearance of the sky is compared to molten brass, or, as some understand it, like the dregs of oil. What is conveyed by the metaphor is that the beautiful blue sky will melt away.