The different colours of the Witch Garte carry a special meaning. Green is the colour of fairies, red is protection against bewitchment and silver is associated with the moon.
In modern witchcraft the witch garter is considered the ancient emblem of the high priestess.
In some traditions a high priestess who becomes Queen Witch over more than one coven adds a silver buckle to her garter for each coven under her.
It is also used in the use of "lithomancy", a type of divination where 13 stones are cast inside a witch garter.
A Witches' Bible: The Complete Witches Handbook
WITCHCRAFT
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