Boil the eggshells por 5 minutes in order to clean them, then put them in the oven for 15 minutes low temp to dry them. Grind the eggshells in fine particles.
A day before, prepare a 2% alginate solution by mixing 200ml of water with 4 grams of alginate. Leave the alginate solution to hydrate for 24 hours.
Mix the eggshell with 20 grams of the hydrated 2% alginate solution. Stir gently until they mix completely avoiding the incorporation of bubbles.
Put in a mold and then pour gently on top the vinegar. It will start reacting and coagulating. Leave it react for 15 minutes and then try to separate the mix from the mold gently in order to leave space for the vinegar to penetrate the sides. Wait for an hour. Then take the sample out of the mold and turn it around to allow the vinegar to reach the other side of the biocomposite. Leave it for an hour more.
Take it out of the mold, rinse it under tap water to clean the vinegar and leave it to dry.