An aspergillum (less commonly, aspergilium or aspergil) is a liturgical implement used to sprinkle holy water. It comes in two common forms: a brush that is dipped in the water and shaken, and a perforated ball at the end of a short handle. Some have sponges or internal reservoirs that dispense holy water when shaken, while others must periodically be dipped in an aspersorium (holy water bucket, known to art historians as a situla).
An aspergillum is used in Roman Catholic and Anglican ceremonies, including the Rite of Baptism and during the Easter Season. In addition, a priest will use the aspergillum to bless the candles during candlemas services and the palms during Palm Sunday Mass. At a requiem, if a casket is present, the priest will sprinkle holy water on the casket. The aspergillum can be used in other manners where sprinkling of holy water is appropriate, as in a house blessing, in which the priest might bless the entry to the home. The name derives from the Latin verb aspergere 'to sprinkle'.
The form of the aspergillum differs in the Eastern Orthodox Church. In the Greek Orthodox Church the aspergillum (randistirion) is in the form of a standing vessel with a tapering lid. The top of the lid has holes in it from which the agiasmos (holy water) is sprinkled. In the Russian Orthodox Church the aspergillium is in the form of a whisk made of cloth or hair. Sometimes, sprigs of basil are used to sprinkle holy water. In some of the Oriental Orthodox Churches, no aspergillum is used, but the priest will pour holy water into the palm of his right hand and throw it on the faithful.
Leviticus Chapter 14
“3. ‘And the priest goes out of the camp and the priest looks, and beholds that the sore of the leprosy of the leper is healed.’ 4. ‘And the priest commands, and takes, for the one healed, two unblemished live birds, cedar wood, Coccus scarlet, and hyssop.’ 5. ‘And the priest commands, and slaughters the one bird in a pottery vessel upon living water.’ 6. ‘He takes the live bird and the cedar wood and the Coccus scarlet and the hyssop and dips them and the live bird in the blood of the bird slaughtered upon the living water.’ 7. ‘And sprinkle seven times upon him purified of leprosy, and he is purified, and sends the live bird upon the face of the field.”
http://en.wikipedia.org/wiki/File:Aspergillum_by_Julia_O%27Gara.jpg#filelinks
An aspergillium is also used by some Wiccans and other Witches to cleanse the ritual area (known as a Circle) prior to one of eight seasonal rituals, known as Sabbats, or a spell. Lunarized water, saltwater, or rainwater is used as opposed to Christian holy water.
Aspergillus, a genus of mold, was named in 1729 by the Italian priest and biologist Pietro Antonio Micheli. When viewed under a microscope, the mold cells were said to resemble an aspergillum.