True alchemy is the practice of turning common metals into gold and trying to concoct an elixir of everlasting life or curing sickness/diseases. Jenario’s alchemy is based upon the same principles. But instead of trying to turn metals into gold, he tries to study herbs for conjuring potions and liquid-based ingredients to help Nickademis as a doctor.
Jenario also plays around with disenchanting metals (later on) or discovering a way to create dispelling bands for countering harmful magic. This might have been proposed towards negative energy.
Alchemists are needed to come up with practical formulas or the exact intake for which doctors use in their medicines. But the council saw Jenario’s way of doing things closer to the way a magic-user would do it. That’s why they turned against him. Based on some of the backstory we receive while reading one of the chapters, the council made Jenario very nervous while he worked. They were always watching, to the point where his nervous twitch caused his knife his slip and cut his fingers. In the council’s eyes, they probably saw Jenario trying to use blood-magic.