Magic Tallow is both an inherently unlocked research option under the Alchemy tab, and a crafting component used in several recipes, such as the Golem Control Seal. Magic Tallow is created via Alchemy, using rotten flesh as a catalyst with a single aspect of Ignis. Because it can be difficult to obtain pure Ignis aspects before having researched the Thaumatorium and Alchemical Centrifuge or the Essentia Crystallizer, an easy way to create Magic Tallow can be to use nether wart, and to soak up the Herba aspects using dirt to create grass, if one has researched Alchemical Manufacture.
Magic Tallow can also be used to make White Tallow Candles, by placing 1 Tallow on top of another, and a string atop that. White Tallow Candles can be used to reduce Instability in Infusion.