Cascarilla is egg shell powder. In the African Traditional Religions, such as Vodoun (Voodoo), you use Cascarilla to draw Veves. These Veves are a type of magick sigil, which represents the Deity in question. Each Spirit, an Orisha or a Loa (depending upon the tradition you’re working with) has their own, individual, sacred symbol. Those symbols are powerful doorways into the worlds of those Spirits. You will find you need to create various Veves for working with the Orisha of Santeria or Lucumi and the Loa of Vodoun.
Other substances (like corn meal or wheat flour) are appropriate as well; it depends upon the Deity and the type of work you are performing. In certain cases, this is most appropriate substance and it’s what you need to get the job done.
Cascarilla is also great for witch style, chalk spells and is easy to work with on surfaces like sidewalks and walls. Use it for magick on the go. It is an important spiritual cleansing agent in several traditions, such as Lucumi and used in baths and in other ways, as well. See also, Uncrossing Bath Mix.
Much like the sand mandalas of the Tibetan monks, Veves are impermanent images. The Spirits require them to be drawn on the ground, on floors, on various surfaces, all with the understanding that they will not last forever. There is thus a certain poetic beauty to working with this material and with this type of magick.