Extract chitin from your shellfish by diluting your shell in 10 percent sodium hydroxide and heat to 80 to100 degrees. This will make the shell water-soluble. Chitin is a mineral compound found in the shell. Once it is soaked and heated it will look like fine grains, identifiable under a microscope.
Remove the calcium carbonate by allowing the chitin to soak in a petri dish of 1 percent hydrochloric acid at room temperature for 10 to 15 minutes. Calcium carbonate will dissolve completely, leaving behind the chitin.
Dissolve your chitin in less than 40 percent sodium hydroxide. Heat to a temperature of 90 to 120 degrees with a bunsun burner. This removes 65 percent of the acetylic groupings to allow them to dissolve during preparation, forming the chitin into chitosan.
Mix chitosan with deionized water, matching the weight to the amount of water required. This will neutralize the chitosan and prepare it for use. When using chitosan for makeup production, do not weaken with sodium hydroxide.