User blog comment:Obsideon/RARITY?/@comment-4829477-20120220165548/@comment-4583259-20120220203444

For deciding what the ratings should be, I'd prefer to use Scooter8pie's Rarity of Uncommon Materials, because it reflects a player's experience better than my chart. However he doesn't list all 42 materials so you'd have to go from my chart for the rest.