Hey @jarc! Welcome to Curiosity. The only way you can sink normal ice is by increasing its density by adding foreign materials like tiny iron pellets in it while freezing. Alternatively, you could try heating up the water enough to lower the density of it so that the ice sinks in it. In this case, you would need to superheat the water above its boiling point of 100 °C.
Caution: Don’t try this! The superheated water will boil violently the moment you introduce ice into it. More on this here.
