Black Soil (黑土）is Ink, an ideogram character.
Here the Black is black charcoal. Ancient Chinese smashed charcoal and mixed with pine gum to make ink sticks. The character meant Ink sticks, not the liquid ink. It means Ink liquid right now because people don't use ink sticks anymore except some (not all) Chinese calligraphists and Chinese painters
Why didn't ancient Chinese call them Ink Stones, but Black Soil? I think the reason is because at the early time, people didn't know to add pine gum, or donkey-hide gelatin to the charcoal so the ink sticks were as loose as soil. As time past, people know how to make solid ink sticks with pine gum or donkey-hide gelatin.
The small seal script for Ink
The clerical script for Ink is
The song typeface for Ink is
Its Pinyin is Mo4.