A pentacle is a talisman or a magical object, typically drawn on the ground and inscribed with a pentagram or another figure. It is used in magical rituals.
Merlin, following the instructions of a grimoire called "The Art of Necromancy", drew one on the floor of Gaius' chambers with silver paint. The circle had a spiral shape and eight dots on the last line. The young warlock then enchanted it with the spell: "Onluc þa soþan treow", and the circle glowed as if it was heated.
Merlin enchants the pentacle.
This pentacle allowed him to reveal the true essence a shade that, thanks to Morgana's necromancy, had taken on the form of Sir Lancelot. When the knight walked into the pentacle, it emitted numerous ghostly screams and Lancelot's face was revealed as the one of a skeleton.
Although it wasn't used for an evil purpose, this form of magic can be considered as dark magic, for it's very close to necromancy, the most dangerous of all sorcery (Lancelot du Lac).
Trivia
The pentacle Merlin created had almost the same form and drawing of the magical coinMorgana had been given by Morgause. This is probably because the two
The illustration of the magical pentacle.
sorcerers (Merlin and Morgana) were practicing the same form of magic, related to necromancy and shades. It's unknown if this pentacle could be used to summon a spirit, too.
