Myself Aida Santana
To make the eggshell powder, gather as many eggshells as you need. Wash them with water and then boil them for about 15 minutes to kill all the bacteria. You may see a white foam on the surface, you can remove this with a spoon. Strain the water and put the eggshells in a tray. You can let them dry at room temperature or if you want to speed up the process put them in the oven at 120 degrees for 15-20 min. Take them out of the oven and when they are completely dry grind them to a fine powder in a grinder. *If you want it to be more uniform you can sieve the powder at the end.
In a pan add the potato starch and the water and stir well until there are no lumps and the starch is completely dissolved.
Heat the solution over low heat and stir constantly until it becomes a thick, translucent paste. It takes about 5 min if using the same quantities as here. *If you have a thermometer you will notice that at 60 degrees it begins to thicken and at 65 it will look more translucent and is ready to remove from the heat.
Remove from heat and add the eggshell and glycerin. Mix well until there are no lumps and a viscous, sandy paste is reached. *If you wish to add color you can add a few drops of food coloring or natural dye.