Recently, friends were over when Lala, Finnian, and friends began rubbing sidewalk chalk into "fairy dust." One of my friends commented that her daughter did that at home, too, and since they were always running out of chalk, one of the fun projects they sometimes do is to make chalk. It sounded right up my ally, so I asked how. Super simple...mix paint pigment, plaster of paris, and water until it is akin to soft serve ice cream. Put it into some sort of container. We used little mixing cups Mike had in his workshop, but ice cube trays would work, too. Set them out to dry in the sun. When hard, play!
(I used the same paint pigment that I use for milk paint. I bought it here and have been so pleased.)