I'm curious how this 1000+ year-old Scandinavian form of hair dying would effect someone's skin or hair, after having completed the process. Were the ingredients of this bleach organic? Was the practice unhealthy for one back then?
From what I understand, the vikings used strong soaps with high lye content to bleach their hair (http://www.vikinganswerlady.com/hairstyl.shtml, http://www.history.com/news/history-lists/10-things-you-may-not-know-about-the-vikings). This link describes the effects of using lye to bleach your hair, but I'm hardly an expert when it comes to ancient hair styling, so I can't vouch for the accuracy: http://www.hairfinder.com/hair4/ancient_hair_lightening_techniques.htm
Doesn't sound like something I'd like to try :). If you're interested about ancient cosmetics and the like, then you should also check out a book called "The Trotula". It's a bit later than viking age, but it has some very interesting recipes for hair care, hair colouring, and skin care. I think there are scans on Google books.