Add salt to hot water and stir continuously until the salt no longer dissolves no matter how much you stir. The salt no longer dissolves, and the salt water at this time is called saturated salt water, and the excess salt sinks to the bottom of the cup.

Then pour the saturated salt water solution on the plastic lid, try to pour it evenly, don't pour too much, just spread a thin layer on the lid.

Place the plate filled with salt water in the sun for a period of time to allow the water to evaporate, and the crystal is completed.