Dark Water

From Tardis Wiki, the free Doctor Who reference
A Cyberman is revealed from a vat of Dark Water. (TV: Dark Water)
You may be looking for the television story or the comic story.

Dark Water was a liquid through which only organic matter could be seen. It originated on Regnidorch II. (GAME: Hidden Mysteries)

3W used Dark Water to hide the cybernetic suits which kept the skeletons of the dead intact, portraying the bodies of the deceased in their organic forms and allowing Missy to hide an army of Cybermen. (TV: Dark Water)