In a traditional Scottish wedding custom, what is “blackening” intended to do to the couple?

In a traditional Scottish wedding custom, “blackening” is intended to cover the couple in a messy mixture.

Friends may seize the bride, groom, or both and cover them with substances such as treacle, flour, soot, feathers, syrup, or other sticky materials. The couple is then sometimes paraded through the community. The custom is associated with comic humiliation, public attention, and the idea that enduring an unpleasant experience together prepares the pair for married life.

Blackening is most strongly associated with parts of Scotland, especially the northeast, rather than being a universal Scottish wedding practice. It may occur before the wedding or around the time of the ceremony. It is also distinct from a formal cleansing ritual: despite the name, the point is not to make the couple spiritually black but to create a deliberately conspicuous mess.