If you are dealing with a villager cartographer, a recipe is displayed which requires copper with an EMC of 128. You can craft this but as soon as you close the inventory and open it again, the copper is converted back into copper with an EMC of 256 and you cannot trade it.
If you are dealing with a villager cartographer, a recipe is displayed which requires copper with an EMC of 128. You can craft this but as soon as you close the inventory and open it again, the copper is converted back into copper with an EMC of 256 and you cannot trade it.