Salt ice fishing

Panel 1, "FAST: salt ice hug". On the left is the bowl: water with lots of ice cubes floating in it, the string draped over them, and a "tiny pinch of salt" where the string touches a cube. The cubes float mostly under water, with just their tops out. The circle is a magnifier on that spot.

The window on the right is a slice through the string lying on top of a cube. Above is air. The string is the bundle of tan circles, its fibres cut across. Under it is a thin wet film on the ice, drawn much thicker than it really is so you can see its colour.

Frame ①. Salt sits in the film, next to the string. Salt melts a thin bit of ice: see the teal dip under the string, "salty water melts ice". Melting takes heat. The salty spot pulls that heat from whatever it touches, the ice under it and around it. That is what the dotted arrows show, "heat soaks in". So that little spot ends up colder than ordinary freezing, below 0 °C. (If you want the name: freezing-point depression. Salty water stays liquid below 0 °C.)

Frame ②. The dashed arrows run sideways inside the film, away from the string: "salt spreads away". The salt spreads out into the water around it. Now the water right at the string is much less salty, so its freezing point climbs back up toward 0 °C. But the spot is still colder than that, so it freezes.

That is the white ice with the orange outline, "new ice grips string". It fills the dip where the meltwater was and wraps around the bottom of the fibres, locking them in. That is the ice hug, and why you can lift a cube by the string.

That is also why the steps matter. A tiny pinch is enough. A mountain of salt keeps everything salty, so it just digs a puddle and nothing refreezes. Water in the bowl helps, because cubes stay wetter at the contact line. Draping over many cubes raises the odds. Pulling slowly keeps fresh ice bridges from snapping.

Panel 2, "LONG: wire squeeze". On the left, the ice block sits on an upside-down container, with the copper wire across it and a bottle hanging from each end ("bottles hang"). The wire has already sunk partway in, and the orange line above it is the path it left. The magnifier is on the wire. The window on the right is a slice across the wire, deep in the ice.

The big solid arrow is the "bottles pull": the bottles squeeze the wire down onto the ice under it. That squeeze lowers ice's melting point, just a tiny bit. It works only because ice in a kitchen is already sitting right at 0 °C, so even a tiny nudge tips it over. Two water bottles on a thin wire press with a few atmospheres, which lowers the melting point by only a few hundredths of a degree. That is enough for the ice right under the wire to turn to water: the thin blue film, "squeeze: melts".

The dashed arrows show that water slipping around both sides of the wire to the top ("water slips around"). Up there it isn't squeezed anymore, so it freezes again: the white strip with orange edges, "refreezes above". The wire sinks, and the block closes up behind it. The block can stay one piece even after the wire is all the way through.

Here is the part that is easy to miss. Melting ice takes heat, so where does the heat come from? Water gives off heat when it freezes. The dotted arrow inside the wire shows that heat, from the refreezing on top, traveling down through the copper to melt the next bit underneath ("heat flows down the copper"). Copper is great at carrying heat, and that is why it works. Warm room air leaking in along the wire helps a little too. A string would barely cut, because it doesn't carry heat.

Room-temperature copper is not a hot knife. It is a heat bridge from the top of the wire to the bottom. (If you want the name: regelation.)