It can be crafted in your Crafting Menu (default key "Q") or at Crafting Tables (that still exist in worlds created before R22 on September 16th 2015), but only after the crafting-recipe has been unlocked upon taking / crafting a Block of Goo for the first time (unlocked by taking a Glob of Goo). To craft 8 Purple Blocks of Goo, you'll need (as of R29 in February 2016): * 2 Globs of Goo (loot or pet-harvest from many Creatures including Pigsies * 1 Stone Rod made of Stone, Limestone or Bedrock in a Processor * 1 Blue Pigment made of Blue Flowers from Elderwood-trees in a Processor