Marsiliano Ficino describes the sol niger as thus-
"There now remains the second part of the physical praxis, the far harder indeed, and far more sublime. In which we read that all the nerves of wit, and at length all the races of the mind of many philosophers have languished. For you would with more difficulty make a man revive, than put him to death. Here the work of God is required. It is indeed the greatest mystery to create souls, and frame an inanimate body into a living statue. Do you not think it is the business of a sprightly Wit to reduce the soul to the spirit, then the spirit to the soul, then again those two to the body? In this body of ours, it is requisite to know, how much the spirit is, how much the soul, and how much the body. Furthermore how much of the soul the middle nature, is in the spirit, and how much in the body, that by this you may join as it were two natures of the same kind, and akin to one another in due proportion. We ought therefore to join two waters, the Sulphur of Gold, and the soul and body of its Mercury, Sol and Lune, the male and female, two sperms, heaven and earth, and two, as I may say, Argent vives, and out of which alone the philosophers say their stone is made; which pitiful fellows mistake for crude mercury. But that mercury is all metals, male and female, and an hermaphrodite monster in the very marriage of the soul and the body, which I call solution; and the putrefaction of the philosophers. The earth of gold is dissolved by its own spirit, which you shall discover in these proportions. The body must be dissolved in the subtlest middle air: The body is also dissolved by its own heat and humidity; where the soul, the middle nature holds the principality in the colour of blackness all in the glass: which blackness of Nature the ancient Philosophers called the crows head, or the black sun.
From whence a certain person advanced this proposition. I saw three circles encompassing one another, three suns in the firmament having three faces, that is, a black, a white, and a red sun. That blackness was also called by the name of all black things; after which all the colours of the world, which can be conceived by wit, use to appear, which at length are brought to a true whiteness, as to a center and principle point. In white there are all colours, and from that the rest seem, as I may say, to be coloured. White and black by Nature herself are colours, and indeed the extremes, out of the manifold mixture and proportion of which with one another we believe the middle colours, as they are called, to arise."