These two special lenses are the only way to read the Codex of Ultimate Wisdom, which resides in the Ethereal Void. The blue lens is for the humans of Britannia, the purple lens for the gargoyles. The convex gargoyle lens is old, having been crafted by Naxatilor and Lor-wis-lem many centuries ago to draw the Codex from the Void. At the time of the False Prophet it was broken and resided in the museum. The Avatar had to get Lor-wis-lem to repair it, so that the lenses could be used to end he war between gargoyles and humans.
The concave human lens is a much younger creation. The Avatar asked Ephemerides of Moonglow to craft it; the magical nature of the lens requiring that it be fashioned from melting down a glass sword.
Both lenses were used together with the Vortex Cube, the eight moonstones, and the Eternal Flames of Infinity and Singularity to return the Codex to the Void. Human or gargoyle can still read the Codex at the shrine with both lenses.