I confirmed this after seeing it in a LOTRO forum post. You can turn housing items from Gorgoroth Steel-bound lootboxes into ashes if you don't want the item.
You can see how many ashes you can get by using your Flame of Ancalamir and clicking on the item. You can cancel if you want to keep it.
Based on items I tried, it looks like you get 80 Ashes of Enchantment for rare/purple items, 120 for incomparable/teal items, and 240 for epic/gold items.
You can also turn tier 10 essences into ashes, 40 ashes for an Empowered Shadow essence, 80 for an Abyssal essence. You probably don't want to do that, since tier 10 essences can be exchanged for one or more Malleable Essences, which can be used to craft better essences or sold/traded.
You cannot convert pet tomes into ashes.