What is dark dull and rough? Something that is a good absorber of radiant energy?

Answer 1

Something made of cast iron -- like a cast iron skillet or camping pot.

Answer 2

Carbon such as lampblack (the black stuff that forms when you hold a candle flame against something) absorbs almost all the light that hits it. Sprinkled on snow even on a very cold sunny day it will melt down through the snow because it's absorbing so much sunlight.