Fostered by the Dominican Order. The general of that society, however, can give to other priests the faculty of blessing it. It was approved on November 23, 1903 by Pope Pius X who granted an indulgence to the wearers every time that they devoutly kiss it. It is made of white wool, and usually bears a picture of a kneeling Saint Dominic on one part and that of Blessed Reginald receiving the habit from the Mother of God on the other.
New Catholic Dictionary and Catholic Encyclopedia