It is a tradition that seems restricted to the rural areas of North East of Scotland and some parts of Northern Ireland. Solely the Bride is blackened in Aberdeenshire, but further north in Scotland both the Bride and groom are Blackened. It started about 200 years ago has been going on for several generations, but getting more messy.
It is quite extreme but the people in these areas seen keen to continue this tradition.
People in other parts of Scotland have often never heard of this.