minecraft-assets/assets/minecraft/atlases/shield_patterns.json

{
  "sources": [
    {
      "type": "minecraft:single",
      "resource": "minecraft:entity/shield_base"
    },
    {
      "type": "minecraft:single",
      "resource": "minecraft:entity/shield_base_nopattern"
    },
    {
      "type": "minecraft:directory",
      "prefix": "entity/shield/",
      "source": "entity/shield"
    }
  ]
}