Science And Magic From Hogwarts Chapter 178

After arriving at Hogsmeade, Asher went straight to the three alchemists, then called Kreacher and took them back to the old house.

First, he ordered Kreacher to prepare three guest rooms for them, and then took them to three different alchemy rooms in turn.

Each person has a blueprint and refines his own part.

The restrictions of the oath have eliminated the possibility of communication between the three.

So they only know what they have done, but they have no idea what the final product will look like or where it will be used.