Case Hardened blue gems: how the pattern works and the famous seeds

Case Hardened is one of the oldest finishes in Counter-Strike and the subject of some of its biggest trades. Every copy uses the same multicoloured texture, and the paint seed decides how much of it shows as blue. The rare seeds that turn the visible side of a weapon mostly blue are known as blue gems.

Where the finish comes from

Case Hardened arrived with the Arms Deal update on August 14, 2013, in the original CS:GO Weapon Case, on the AK-47 and the first knives. The in-game description says the metal "has been color case-hardened through the application of wood charcoal at high temperatures", a nod to a real-world gunsmithing technique.

Three guns carry the finish today, according to the game's item definitions:

AK-47 | Case Hardened, from the Arms Deal Collection (the CS:GO Weapon Case).
Five-SeveN | Case Hardened, from the Arms Deal 2 Collection.
MAC-10 | Case Hardened, from the 2021 Dust 2 Collection.

It is also available on every knife model, from the Bayonet to the Kukri, and on one pair of gloves, the Hydra Gloves. The finish covers the full float range from 0.00 to 1.00, so every wear tier exists.

How a seed becomes a blue gem

The Case Hardened texture is a large sheet of blue, gold and silvery patches. The paint seed shifts and rotates that sheet on the weapon, so each seed shows a different slice of it. Most slices are a mix of gold and silver with some blue. A small number land a solid area of blue across the parts of the item you actually see. The pattern index guide explains the mechanism in more detail.

Three things follow from how this works:

Float doesn't change the colours. Wear scratches the surface but leaves the blue, gold and silver layout in place, so a Battle-Scarred blue gem is still a blue gem. It is simply worn.
Seeds are specific to one skin. The texture is scaled differently for each model, so a top seed on the AK-47 means nothing on a Karambit.
The visible side matters most. For knives, collectors judge the play side, the face you see when the knife is held. Dot Esports describes a loose baseline of around half the play side being blue before a Karambit counts as a blue gem, with top seeds near full coverage.

Collectors sort seeds into tiers, and Dot Esports notes that different sources draw the tier boundaries slightly differently. Patterns that come out almost entirely gold are sometimes called gold gems, but they sell for far less than blue ones.

The famous seeds

AK-47, seed 661. This is the seed most often named as the best blue gem on the rifle. Dexerto reported in April 2023 that a StatTrak Minimal Wear copy with four Katowice 2014 Titan Holo stickers sold for around $400,000, as part of a combined deal worth more than $500,000. On June 5, 2024, esports.gg reported that a StatTrak Factory New 661 with a 0.04827 float had sold for over $1 million. The exact figure was not disclosed.

Karambit, seed 387. Dot Esports, in a guide updated in August 2026, describes 387 as the consensus top Karambit pattern, with a single known Factory New copy at a float of 0.048. In September 2021 its owner turned down a private offer of 1.2 million euros in Bitcoin. Figures quoted for it since then are estimates built on that rejected offer, not a completed sale. The same article reports that a Well-Worn 387 sold for $118,000 in June 2023, and that a claimed second Factory New copy surfaced in late 2024 whose authenticity is still debated.

These stories also show how much the rest of an item matters. The 2023 AK was worth far more with its four Katowice stickers than it would have been bare, and the 2024 sale was driven by the rare combination of StatTrak, Factory New and the top seed.

The finish on knives and on Hydra Gloves

What the 2025 trade-up change means

Since Valve's October 22, 2025 update, five Covert skins can be traded up for a knife or gloves from a collection of one of the inputs. The pattern of the result is random, so there is no way to target a blue gem this way. What the change did do, according to Dot Esports, was add a wave of new knives to the market and push knife prices down, while top-tier blue gem Karambits mostly held up. The trade-up guide covers the rules.

Checking a Case Hardened before you buy

Read the seed yourself. Inspect the item in game and note the Pattern Template. Screenshots and renders can be flattering, and lighting changes how blue reads.
Use a list for the exact item. Compare the seed against a tier list for that weapon or knife model, not the finish in general.
Look at the right side. On knives the play side carries most of the value, though a strong blue back side is a bonus. On the AK-47, collectors also weigh where on the rifle the blue sits.
Price the whole item. Wear, StatTrak and stickers all move the price, as the 2023 AK sale shows.

On CS2Sell, the blue percentage filter on Buy narrows Case Hardened listings by how much blue they show, and the paint seed filter lets you search for a specific pattern number from a tier list.