As used in sympathetic magic
Also known as Visitation, Wishing, or Manifestation Boxes, they were used in sympathetic magic.
The spell was instigated by placing small tokens inside the box representing the wishes or desires of the owner. These items could include strands of hair, personal possessions, pieces of paper bearing written spells, symbols or talismans, or even hand drawn representations of the desired outcome. These ingredients would be wrapped in cloth, along with significant leaves, nuts or flowers, as the spell dictated
Tradition had it that the spell was performed at a time auspicious to the intent. A few words, or a rhyme would be recited as the items were placed in the box. The the box would then be tied with red string, or sealed with wax of the same colour. It would then be hidden, sometimes being buried beneath, or close by, a path the intended recipient of the spell was known to walk. The magical package might also secretly be taken to an special auspicious, or magical place, a holy well, or wishing tree.
The various names - shadow, visitation, and manifestation - of the boxes suggest a belief that a fairy, or spirit of some kind was the agent by which the magic would be executed. The fairy would be attracted by the magical essence of the box, and carry out the owners wishes.
The boxes themselves might be specially constructed for the purpose of the spell, either at home of by a local wise person. Indeed it was often the case that a wise person was consulted, who then prepared the Shadow Box, and provided full instruction on how complete the spell.
The tradition of Shadow Boxes making seems to have declined rapidly with the rise of industrialisation, there are only a few wise men or women remaining with the knowledge of their use.