Gopī-candanam — The Sacred White Clay of Vaiṣṇava Devotion
Gopī-candanam (gopī = the cowherd women devotees of Kṛṣṇa at Vṛndāvana/Dvārakā; candana = sandal/paste — though here it refers to the white clay rather than true sandalwood; 'the clay/paste of the gopīs') is a specific white clay obtained from Gopī Tālāv ('the Gopī Lake') near the sacred city of Dvārakā on the western coast of India (modern Gujarat). According to the devotional tradition enshrined in the Purāṇas and Vaiṣṇava hagiography, this lake is sacred because it is the place where the gopīs — Kṛṣṇa's devoted women companions — once immersed themselves in the waters in intense longing for Kṛṣṇa after His departure from Vṛndāvana to Dvārakā. The white clay of this lake bears the impression of Kṛṣṇa's feet from when He visited the gopīs there; applying this clay on the forehead is, for the devotee, to wear the mark of Bhagavān's feet upon oneself.
In North Indian Vaiṣṇava traditions (Puṣṭimārga, Gauḍīya Vaiṣṇavism, and others), gopī-candana clay is used to apply the ūrdhvapuṇḍra mark — the vertical Vaiṣṇava sectarian mark on the forehead — as well as marks on the arms, chest, neck, and back. The twelve body marks (dvādaśa-tilaka — marks on twelve body points including the forehead, throat, chest, navel, arms, and back) each represent one of the twelve names/forms of Bhagavān Viṣṇu and are applied with either gopī-candana clay or ūrdhvapuṇḍra paste before worship. In South Indian Śrī Vaiṣṇava tradition, the equivalent sacred clay is called tirumāṇ (tirumaṇ — 'the sacred earth/clay') or śrī cūrṇam and is applied in the characteristically South Indian ūrdhvapuṇḍra form: two vertical white lines on the forehead with a red line (śrī cūrṇam) in the center representing Bhagavān (white) and Mahālakṣmī (red) together.
The use of white clay (tirumāṇ or gopī-candana) rather than ash (bhasma, the mark of Śaiva practitioners) is the most immediately recognizable external distinction between Vaiṣṇava and Śaiva practitioners in the South Indian tradition. The Āchāryas teach that the ūrdhvapuṇḍra mark is not merely a sectarian identifier but a theological declaration: the two vertical lines represent the two feet of Bhagavān Nārāyaṇa; the red mark in the center represents the Lotus-seated Mahālakṣmī who resides in Bhagavān's chest. To mark the forehead (and the body) thus is to consecrate oneself as a vessel of Bhagavān's and Mahālakṣmī's joint presence — a living walking shrine. In Śrī Vaiṣṇava Āgamic practice, the tirumāṇ is applied each morning after bathing as part of the nityakarma (daily obligatory practices), before any pūjā or meditation.