Hi,
first of all - sorry for my English.
From what I discovered Copper Ore can't be textured with overlay.

Basically, the problem was for me so strange because Cobalt Ore worked with "cube_overlay_all" fine (all: netherrack and overlay: transparent cobalt_ore) but Copper Ore not (all: stone and overlay: transparent copper_ore)
So I cloned the repository and browsed code.

From my research and tests inside WorldCientEvents.java missing:

  static void clientSetup(FMLClientSetupEvent event) {
    (...)
    // render types - ores
    RenderTypeLookup.setRenderLayer(TinkerWorld.copperOre.get(), cutoutMipped);
    (...)
  }

Screenshots:

Behavior with release 3.0.3.144:

Behavior after added missing line:

Versions:

• Minecraft: 1.16.5
• Forge: 36.1.16
• Mantle: 1.6.92
• Tinkers Construct: 3.0.3.126, 3.0.3.144 (so I expect in all previous where copper ore appeared)

Confirm below that this enhancement is not covered on the roadmap or "Whats New?"
Confirmed

That's not our copper ore texture, that's a resource pack. If you tried the same thing on vanilla ores, you'd get the same issue. I honestly don't see much point changing the render type, you can just use a single layer texture for the ore in your pack.

The fact that cobalt.works is leftover legacy stuff and probably will get removed later.