Contrary to popular belief, the wear of a Case Hardened skin has no impact on determining whether a skin is a Blue Gem or not. In fact, the amount of blue color in a Case Hardened skin is determined solely through its pattern index - a number that is automatically set by the system as soon as the skin is unboxed and can’t be changed afterward.

The higher the percentage of blue color present in a Blue Gem, the more highly the pattern index is regarded within the community. Ideally, a Tier 1 Blue Gem should have a full blue playside, with no traces of yellow being present. The amount of blue in the backside isn’t taken into account when ranking Blue Gems in CS2.

A Tier 1 Blue Gem, which features the most amount of blue on the playside, is considered the most valuable, with a correspondingly higher price point. In comparison, a Tier 2 Blue Gem, although still valuable, will have a lower price point than a Tier 1 Blue Gem. Similarly, a Tier 3 Blue Gem will be less valuable than a Tier 2 Blue Gem, and so on. Therefore, the rank or tier of the Blue Gem is an important factor in determining its value, even though it is still dependent on a variety of other factors as well.

This guide shows only Blue Gem Playside patterns. There is also a guide for Skeleton Blue Gem Backside only.
https://steamcommunity.com/sharedfiles/filedetails/?id=3415171994

456, 169, 681, 316, 577, 58

704, 55, 281, 922, 668, 449, 556, 351, 447, 583, 262, 180, 880, 210, 345, 850

634, 124, 601, 496, 170, 915, 585, 916, 67, 628, 383, 239, 698, 372, 533, 336, 588, 442, 202, 837, 166, 116, 700, 954, 187, 797, 429, 632, 529, 516, 157, 547, 14, 294, 103, 525, 624, 503

269, 393, 288, 430, 374, 669, 507, 887, 179, 828, 867, 812, 162, 959, 941, 10, 853, 387, 820, 299, 640, 818, 902, 776, 606, 417, 872, 91, 680, 955, 537, 286, 176, 693, 107, 899, 13, 203, 719, 151, 88, 879, 821, 519, 298, 222, 349, 212, 227, 715, 750, 325, 84, 805, 504, 235, 807, 241, 740, 878, 619, 292, 910, 689, 675, 334, 866, 651, 911

https://steamcommunity.com/sharedfiles/filedetails/?id=2948564018

https://steamcommunity.com/sharedfiles/filedetails/?id=2948578790

https://steamcommunity.com/sharedfiles/filedetails/?id=2948645553

https://steamcommunity.com/sharedfiles/filedetails/?id=3090086681