Chocolate bloom is the white substance that is seen on chocolate. It is caused from drastic changes in temperature or from not being stored properly. It does not affect the taste of chocolate, but isn’t very pretty. It’s the cocoa butter (or oils) in the chocolate making their way to the surface. If you are melting your bloomed chocolate down, it will all mix back in place and will be fine for dipping or molding.
Read more here: http://blog.gygi.com/blog/2012/02/16/chocolate-101-bloom/