Anandakanda 1.23.101

1.23.101

tāṃ mūṣāṃ gaḍḍukāyantre pacenmandāgninā dinam /
rasabhasma bhaveddivyaṃ sindūrāruṇasannibham //

that crucible in a gaḍḍukāyantra and cook it with a mild fire for a day.
It becomes a divine mercury calx, resembling the dawn color of red lead,