Writing fluids (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">writing fluids</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for inks that I've seen before include "Sink beneath writing fluids" , "Liquids used for printing" , "Fluids from cuttlefish" , "Printers' media" , "Printing fluids" .)