Metals in the Goetia

[PsychoNox]

When doing a summoning in the goetia. I can understand making the seals in the corresponding metal of the Demon you are summoning. But what im curious about is what about those who say you must make them in Mercury? IF im not mistaken is it not in liquid most of the time?

What is the best alternative when making the talismans of the spirits of this planet if ever

thanks and Bright blessings
LVX