What is purpose/reason of using Thiruman katti for making Urdhwapundra or Namam, What is relation of Thiruman to Shriman Narayana? How is it holy clay?
Thiruman, is etymologically speaking, 'holy clay' from tiru, 'holy' and man, 'clay'.
It is a tilaka, a mark on the forehead, that is worn by followers of Sri Vaishnavism tradition, that is followers of Vishnu.
Visually, the tilaka is a yellow or red mark in the middle of the white marks. The latter marks are called thiruman in Tamil, whilst the former is called srichurnam.
Here, sri refers to Laksmi whilst churnam literally means powder. This yellow mark is made from turmeric or sandalwood paste. The white powder in thiruman derives from decayed schistose mica, a metamorphic rock formed from shale. It refers to the feet of Vishnu.
It is holy because the feet of Vishnu are holy.
Srimathe Ramanujaya namaha!
Thiruman is obtained from medium grade metamorphic rock. It is defined by having more than 50% platy and elongated minerals. It is found mainly in Melkote, Karnataka.
Pundraka -(Urdhva pundra in Sanskrit), (Thiruman, or Thirunamam in Tamil) - ritual mark, means holy mud, is applied on the foreheads of devotees of Sri Narayana, and Lord Vishnu himself wears it on His forehead.
Devotees apply it as a mark of respect to Lord Vishnu, denoting they are holding His Lotus Feet on their forehead. The two white lines represent the feet of the Lord, and the red line represents Lakshmi Thaayar who is ever present with Him. According to other sources, the left line represent Lord Brahma, the right line Lord Siva and the middle portion is where Lord Narayana dwells with Mother Lakshmi. The meaning of Him wearing it is to show the Bhaktha that the protection to him is from all possible direction, if he surrenders to the Lord. Each thiruman placed on the body represents a different name of Sriman Narayana:
forehead Kesava belly Narayana chest Madhava throat Govinda right side Vishnu right arm Madhusudana right shoulder Trivikrama left side Vamana left arm Sridhara left shoulder Hrisikesha upper back Padmanabha lower back Damodara