One of the most well documented cases of blacking up in Cornwall actually comes from the Britannia Coconut Dancers of Bacup. Their dances were, reputably, brought up from Cornwall by the Cornish miners who went all over the world in the 17 and early 18th centuries. That is why they black up and wear black trousers and tops and black their hands as well. Another form of guising, would have been to wear masks, but not in this part of the country. Some of the most amazing guise masks I have seen were in the mountains in Bulgaria. The tradition of guising is well documented in Cornwall and other towns, not only Padstow, have guising traditions still which take other forms. E.g. In the twin villages of Kingsand and Cawsand at New Year, just about every single person in the area dresses up and goes out into the streets. If you ask the older people why they do it you might get the answer, 'because my family have been doing this for centuries' and if you ask the teenagers they will tell you it is because 'it has always been done'.   Virtually the same thing but in their own words. If you google mummers in Cornwall you will come up with the words, in dialect, to the 1760 Cornish Mummers Play which has a character called Jambo, who is black faced. He calls for money, ie begging. The original of this is in the Public Records Office in Truro. As I suggested, you might like to look up the excellent references given by Mike on the Wikipedia site which will give you historic authenticity, although as you are still asking for it, I presume you have already looked at them? It also seems that people are confused as to what happens on Mummers day. There is no dancing nor is there a play. A small group of people, about 25 or so, black up and walk through the town playing and singing. The majority of songs they sing are regarded by folkies as 'Cornish' [ and that's a whole new topic]. They have with them collecting tins in which they collect money for local charities or to be given to local families in need, i.e. they walk the streets and go into the pubs, blacked up and guising. In other parts of Cornwall guising would mean dancing through the streets and there are collesctions of Guise dance tunes available from Merv Davey, and Cam Kernewek. Merv is the Piper who leads the Cornish Gorsedd and was honoured as a Bard for sevices to Cornish Music, as was Mike O'Connor. Both of these are eminemt folklorists who have a great in depth knowledge of the music and traditions of Cornwall.