One of the ways of making chalk uses the quicklime powder the is used in the local whitewash paint. When quicklime and water mix, the result is a very violent exothermic reaction that boils the water. Add the quicklime to the water, work in a well ventillated area, and be extremely careful.
    You can get chalk powder from lime powder or by pounding seashells. Mix the powder with water; 4 parts water to every 1 part powder. If you are using lime, be careful.
    You can add colored dies to this mixture to make colored chalk.
    Allow the mixture to stand and settle overnight.
    Skim off the excess water, and pour the resultant sludge into a cloth to let it drain overnight.
    Roll the chalk into snakelike sticks of desired thickness, cut the chalk to desired lengths, and allow the chalk to dry