The AK-47 is the rifle that rewards short, controlled bursts, and Case Hardened skips paint in favor of real metalwork. The steel is color case-hardened by heating it packed in wood charcoal, a genuine hardening process that leaves swirling blue, gold, and silver tones in the surface. Because the coloring comes from the heat treatment, the blue placement varies from rifle to rifle.
Case Hardened skins are tinted by a paint seed, one of 1000 patterns. The seed fixes the blue, gold and purple layout on the weapon, so two Case Hardened of the same wear can look completely different and trade at very different prices.
Seeds with heavy blue coverage on the most visible side are called "Blue Gems". On the AK-47 the best-known examples are seeds like 661, 670 and 955; on the Karambit, seed 387 is the reference Blue Gem. Tier lists rank seeds by blue percentage, and top patterns command large premiums over an average Case Hardened.
Because the seed is not shown in the item name, buyers check the paint seed in the inspect screen or a pattern database before paying a Blue Gem price.
CS:GO Weapon Case
Inspect a WW copy in game 
