Rite of Conquest

The Rite of Conquest is a magical ritual to enhance the power of magical materials by means of a trial.

Whenever a Rite of Conquest is declared and accepted, a sufficiently difficult obstacle must be overcome this will increase the potential of a substance acquired as the price of this contest. The more difficult the challenge the higher the increased potential.

Declaration on such a Rite of Conquest must be made by both parties, the one currently in possession and the one challenging that possession.

Say you want a mause for potion ingrideances and your cat has one currently you could challenge it's possesion of the mause. If you were to overcome your cat and use the mause in your potion it might be just a little stronger.
On the other hand, if you need a dragon's heart for a potion you could look for a dead dragon or maybe have somebody acquire one for you. You could however, challenge a living and healthy dragon for possesion of his heart in single combat and, should you survive such stupidity, you can be sure it will provide you with its greatest effectivness.

The only other way to increase the power of such ingrediances is for them to be freely given.

Obviously there needs to be a sufficient challenge, so climbing up an oak tree to cut mistletoe will not increase its potential...