Cascarones are emptied egg shells dyed, filled with various substances, and the opening sealed with paper. Now the filling is most often confetti, but it may be flour, glitter, etc., and at one time it was perfume. During festivals the cascarones are broken over the heads of unsuspecting victims in the spirit of fun.
It is believed, but not yet documented, that the custom began in Renaissance Italy and migrated from there to Spain, and from Spain to the New World. The progression follows that of the pinata.
While some have speculated that cascarones were brought to the Americas by Maximillian and Carlotta during their reign in Mexico, Richard Henry Dana in his Two Years Before the Mast, observed the custom in California in 1836:
"The great amusement of the evening - owing to its being the Carnival - was the breaking of eggs filled with cologne or other essences, upon the heads of the company. The women bring a great number of these secretly about them, and the amusement is to break one upon the head of a gentleman when his back is turned. He is bound by gallantry to find out the lady, and return the compliment, though it must not be done if the person sees you."
-From SAPL's Texana/Genealogy Department's Fiesta Archives