The molten shard is used to make the artisan's cape and artisan's helm. They are occasionally obtained by players with 99 Smithing when training Smithing. Upon finding one, the following message appears: "You find a shard emanating magical energy during training, and place it in your inventory." When combined with the carved shard (Crafting), designed shard (Construction), fiery shard (Firemaking), fletched shard (Fletching), herbal shard (Herblore), roasted shard (Cooking), and runic shard (Runecrafting), it will turn into the artisan's cape and helm. The cape has the same bonuses as other Capes of Accomplishment but it comes with a different emote and boosts all relevant skills to 100 when operated.
If you do not have space in your inventory, you'll get the message: "You found a shard emanating magical energy as you were training, but there was no space in your inventory to take it." Once there is a free space, the shard will be obtained.
If a player owns the expert skillcape shard bag, the shard will automatically be added to that bag, even if it is in the bank.