Hopefully, you have been customizing your altar and maybe even building other altars for other purposes. This requires 4 beacons to complete the altar as well as 52 more runes (these can be any runes).
With a new Tier of Altar comes another type of Slate. Ethereal Slate can be crafted by placing a Demonic slate into a tier 5 Blood Altar and adding 30,000 per slate. These slates are only used to craft downgrades for the Living Armor as there are no new runes with this Tier Blood Altar.