Please use chips (natural pigments). You can control the ink by adding/ extracting glue from it.
As for ink from inkstick, the left-over ink is called ‘su ink’. This has special effects and are used to create special purposes. We once interviewed one Chinese artist who followed Huang BinHong’s style and uses a lot of Su Ink painting techniques. You might be interested:
Chinese Su Ink landscape painting tips with Wang Zirang
There are differences between fresh-made ink and overnight ink. 🙂 Both are great for creating unique effects. You might want to do some experiments yourself with your papers/ techniques/ brushes. I would recommend you also prepare some natural glue:
Traditional Natural Animal Gelatin 三千本胶