"The chimney sweep, by virtue of his blackened face and his connexion with fire and the hearth, is a very lucky person to meet by chance"
Encyclopaedia of Superstition 1948 E & M Radford, revised 1961 Christina Hole
It was customary to bow or greet a chimney sweep 'in his blacks' - that is to say, when still grimy after his work. In some places, people would spit and make a wish. Apparently, chimney sweeps in Poland and Croatia wear all black and are thought lucky too. You touch a button to attract the magic.
|Sweeps are used as New Year good luck charms in Germany|
This especially applied if a chimney sweep in his blacks should meet a bridal procession. Ideally he should turn and walk along beside the bride to bring her extra good fortune. If he had his back turned, that was a very ill omen.
So nowadays people sometimes hire sweeps to come to a wedding, bringing their good luck with them.
|Black face morris men at Rochester Sweeps Festival c/o Jill Catley|
After all, the hearth was where domestic rituals took place - and soot would be a product of such magical processes as making bread or smelting metal. Soot collected from your hearth could be used in spells against you, it was once believed. Soot could be made into a form of ink to create sigils and other magical writing -even tattoos.
So inviting a sweep to your wedding would seem like a good idea. If nothing else, it makes a good photo opportunity.