Method 1 of 2:
Method 1: Store-Bought Sodium Acetate Method
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Buy some sodium acetate trihydrate. While this material isn't expensive and is non-toxic, it's usually not available in stores, so buying it online may be the easiest way to go. (You can also get it from a squeeze warmer pack.)
If you prefer to make your own, skip straight to the section detailing the homemade sodium acetate method below. Be aware that homemade sodium acetate will result in Slower hot ice made and a dirtier color - if not made properly, it may not even make hot ice.
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Dissolve the sodium acetate trihydrate crystals. Dissolve as much sodium acetate as possible in near-boiling hot water
Scoop out the sodium acetate and place in a saucepan. As you can see in the picture, it is gelatinous because it came from a warm packet, but it should still be powdery in most cases. It's better to start with about a cup portion of sodium acetate at first. Be sure to leave a little outside the pot, which can be used as a crystal seed later.
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Add water to the pot. There should be just enough water to dissolve the sodium acetate. The key is to get the water "full" or "supersaturated" with sodium acetate, so don't add too much water. The less water you add, the more concentrated the solution will be and the better the crystals will be.
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Heat the mixture until it is close to boiling.
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Stir the mixture continuously. This is how the crystals actually dissolve. All of the powder should dissolve into liquid until no more sodium acetate dissolves. In other words, there should still be a little bit of undissolved powder at the bottom of the pot. (If there isn't, keep adding powder until the solution is thick enough.) Remember, you should keep the solution as saturated with sodium acetate as possible. Constant stirring is very important at this stage.
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Once dissolved, pour the solution into any size glass. Make sure the remaining undissolved sodium acetate stays in the pot. Do not pour undissolved ingredients into the glass.
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Let the solution in the glass cool in the refrigerator for an hour or even 30 minutes (as accurately as you can judge for yourself). At this point, you let the temperature drop below what it was when the solution was saturated. Normally, once the temperature is lowered, the easily dissolved crystals will recrystallize. But in this case, because the sodium acetate has formed a supersaturated solution, it has "overcooled", i.e., it has dropped below the normal crystallization temperature, but has not crystallized.
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