Illustration: three CS2 agents kneel in awe around a blue and gold Case Hardened AK-47 on Mirage A site

CS2 Case Hardened patterns and blue gems

Every Case Hardened skin carries a pattern seed, a number from 0 to 1000 that decides where its blue, gold and purple land. Here is how the seed works, what people mean by a blue gem, and how to check any seed on the real model in 3D.

AK-47 | Case Hardened at pattern seed 661, play side, rendered in the SkinsViewer 3D viewer — One AK-47 | Case Hardened at two seeds, Factory New, play side, rendered in our 3D viewer. Seed 661 puts blue across the top cover; seed 69 leaves the receiver and magazine mostly gold.

AK-47 | Case Hardened at pattern seed 69, play side, rendered in the SkinsViewer 3D viewer — One AK-47 | Case Hardened at two seeds, Factory New, play side, rendered in our 3D viewer. Seed 661 puts blue across the top cover; seed 69 leaves the receiver and magazine mostly gold.

What Case Hardened is

Case Hardened is a CS2 finish of blue, gold and purple heat colours on bare metal. The AK-47's own item description says it "has been color case-hardened through the application of wood charcoal at high temperatures", the old steel treatment the finish is named after.

The finish is the same on every copy. Where its colours land is not. The paint comes from one large colour sheet, and the seed decides which part of that sheet ends up on which part of the weapon, so two copies with different seeds can look like different skins. The float is a separate number: it sets how worn the paint is, not where the colours sit.

The pattern seed, 0 to 1000

The pattern seed, also called the pattern index or paint seed, is a whole number from 0 to 1000 that every copy of a skin carries. It never changes, so a seed always gives the same pattern on the same weapon.

On Case Hardened the seed slides the colour sheet across the weapon and turns it, anywhere on a full circle. On many other finishes the seed only moves the wear and grime, so every copy looks alike. Crimson Web is another finish whose seed moves and turns the pattern itself.

Seed: 69
Across: 0.28
Down: 0.59
Turn: 139°

Seed: 661
Across: 0.32
Down: 0.49
Turn: 105°

The seed is a whole number from 0 to 1000. It picks where the colour sheet sits on the weapon: how far it slides across, how far down and how far it turns. The numbers are the placement our viewer computes for each seed; the drawing is a schematic, not the real sheet.

What a blue gem is

"Blue gem" is what players call a Case Hardened skin whose seed puts mostly blue on the parts you look at most. It is not a Valve label: no item in the game is named a blue gem, and the lists of which seeds count are made by players and collectors, so they differ from site to site.

On the AK-47 | Case Hardened, the seed people cite most is 661. Its play side has a blue top cover with a thin gold mark near the front, the "scar" collectors name it after. You can see it in the renders on this page and turn it yourself in 3D.

Seed lists are per weapon. Each weapon wraps the colour sheet its own way, so a seed that is blue on the AK-47 can be mostly gold on a knife. Check the seed on the weapon you care about.

Play side and back side

A weapon has two sides. The play side is the one you see while you hold it in first person; the back side faces away from you. A blue gem is judged by its play side first, since that is what you look at in a match, and a pattern can be blue on one side and gold on the other.

In our viewer the Right view shows the play side, the side the in-game inspect screen opens on, and the Left view shows the back. Switch with the Right and Left buttons under the model, or press 1 and 2. Here are the back sides of the two seeds above.

AK-47 | Case Hardened at pattern seed 661, back side, rendered in the SkinsViewer 3D viewer — The back sides of seeds 661 and 69. Seed 661 keeps blue along the top cover here too.

AK-47 | Case Hardened at pattern seed 69, back side, rendered in the SkinsViewer 3D viewer — The back sides of seeds 661 and 69. Seed 661 keeps blue along the top cover here too.

Check a seed in 3D

Our 3D viewer renders any seed from 0 to 1000 on the real CS2 model, with the same placement the game uses. Open one of the seeds below, or pick a weapon and type a seed.

On any Case Hardened skin page, type a seed into the Seed field: in the Skin panel on a gun, under the viewer on a knife or gloves.
The pattern moves on the model. Turn it with Right and Left to see both sides.
The address in your browser now carries the seed, so you can share the exact pattern you are looking at.

We checked seeds 1, 69 and 661 on the AK-47 against in-game screenshots of the same seeds, and the colours land in the same places. Lighting is not the game's, so compare where the blue and gold sit, not the exact shade.

Seeds in gen commands and inspect links

A gen command carries the seed as its third number, after the weapon id and the paint id. This one is the AK-47 | Case Hardened at seed 661:

!gen 7 44 661 0.01

A masked inspect link carries the seed too, with the float and any stickers. Paste either one into SkinsViewer and the builder opens that seed. A link copied from someone's inventory or the Steam market usually holds only an item id, not the seed, so it cannot be read without a lookup, which SkinsViewer does not do.

Every weapon with Case Hardened

Case Hardened comes on 3 guns and 20 knives in CS2. Hydra Gloves have a Case Hardened finish of their own. Each one opens in 3D with its seed control.