To add a new tool/armor material (ex. Carbon), you can use the KubeJS startup event:
GTCEuStartupEvents.registry("gtceu:material", e => { GTMaterials.Carbon.setProperty(PropertyKey.TOOL, ToolProperty.Builder.of(0, 1, 64, 1).build()) //harvestSpeed, attackDamage, durability, harvestLevel GTMaterials.Carbon.setProperty(PropertyKey.ARMOR, ArmorProperty.Builder.of(10, [1, 2, 3, 4]).toughness(4.0).knockbackResistance(1.0).build()) //durabilityMultiplier, [helmetProtection, chestplateProtection, leggingsProtection, bootsProtection] //Toughness & Knockback Resistance are optional. })
ignoredGTMaterials