There are several wiki pages that refer to blue diamonds that seem to be in opposition:
http://wiki.project1999.com/Jewelcrafting
http://wiki.project1999.com/Enchant_Adamantite
http://wiki.project1999.com/Blue_Diamond
The Jewelcrafting page says Blue Diamond combines are disabled until Velious.
The blue diamond page does NOT refer to the combines for the adamantite, and says its disabled.
The Enchant adamantite page says you need a blue diamond as a reagent.
Which is it?