Before the release of Menaphos on 5 June 2017, soul runes were the only conventional type of rune that could not be crafted using a normal Runecrafting altar. The only way to craft soul runes was by using the Ourania Rune Altar, but this altar forces runecrafters to craft a random selection of runes. There is a soul rift in the Abyss and an obtain soul rune option on the wicked hood.
The mechanics of crafting soul runes vastly differ from the standard Runecrafting process. The altar must first be charged with pure essence by putting pure essence into the 'charger'. Four essences generate one charge and give 10 Runecrafting experience. 1.25 charges create one soul rune. This means it takes 5 essences to make one soul rune. The experience gained is 220 per charge or 275 per soul rune crafted.
The 'Charger' has capacity of 100 essences, after which they must be converted into charges; and the altar can hold up to 100 charges, after which they must be crafted as runes.
To maximise the experience gained, the 250% bonus experience of abyss rune crafting (thus the Demonic Skull too) is applicable to the rune crafting step. A maximum of 77000 experience can be gained by binding a fully charged altar into at least 80 soul runes.