You can pour water straight from the kettle into the trays and cover it. https://www.dreamstime.com/stock-photo-ice-cubes-image1794880 https://www.dreamstime.c

You can pour water straight from the kettle into the trays and cover it. https://www.dreamstime.com/stock-photo-ice-cubes-image1794880 https://www.dreamstime.com/stock-photo-ice-cubes-image179488... In that photo I see a few gas bubbles, but it is dominated by radial expansion fractures and cloudy high pressure ice in the center. That ice will crack when put in water. Clear ice does not crack.