Aug 17, 2019
Bhagavan Atthivaradar is so named because the original idol was made of Fig tree (அத்தி மரம்)। The God (wooden idol) is in a state of Divine sleep in the bottom of the temple tank. Every 40 years the idol is brought to the surface and placed in the Vasantha Mandapam for 40-48 days for the benefit of devotees.
In the first 24 days, the Lord is in his natural recumbent state (Kidantha ThiruKolam Or Sayana Kolam = Natural state or Recumbent posture). He appears in a standing position (Ninra Thirukolam) for the next 24 days for worship by the devotees.
He was the Moolavar (Fixed deity) in Varadaraja Perumal Temple in Kanchi near Chennai.
In the 16th century CE, the idol was stored in the temple tank to protect it from foreign invaders.
Updated: 17 Aug 2019, 03:44:00 PM
Atthivaradar festival ended. Today the immersion ceremony into the temple pond takes place. Before the immersion, the Thaila Kappu ( Oil preservation).
Thaila Kappu: Oil Preserve. Why Apply it to Athi Varadar Wooden Idol Before Keeping In Temple Pond?
Thaila Kappu:
Thaila Kappu (Oil preserve) How is the oil made to protect and preserve Atthivaradar immersed in the pond? Varadaraja Perumal Koil Bhattar explains.
Athi Varadar Thaila Kappu
Atthivaradar, having granted grace to the devotees, is about to enter and sleep in the Ananda Saras pond this evening. The Bhattar of the temple explains the preparation of the infused oil for the preservation and protection of the idol.
The Atthivaradar festival took place from 2019 July 1 to August 16. Ten million seven hundred thousand people participated and received Darsan of Atithivaradar, according to Kanchi Divisional Manager Ponnaiya.
Again back into the pond.
After 48 days of emersion, Atthivaradar will go into occultation in the temple pond on the evening of August 17, 2019, at 4 PM. Before the re-immersion, worship of the Bhagavan took place. At 10 PM in the previous night, Oil preparation was applied to the idol.
Do you know what all are present in the occultation temple tank?
The idol of the Atthivaradar Perumal enters the temple tank to remain for the next 40 years.
Here is the preparation of the Oil Preserve. Pacchai Karpuram, Lavangam, Elakkai, Sambrani, Sathikai, Vetti Ver, and Santhanathi oil are heated. The oil is filtered and applied to the idol of Atthivaradar. This Oli Preserve makes the wooden idol stronger. 
 Pacchai Karpuram1, Lavangam2, Elakkai3, Sambrani4, Sathikai5, Vetti Ver6, and Santhanathi Thailam7= Edible Camphor1, Clove2, cardamom3, frankincense4, nutmeg5, Cuscus grass6, Sandalwood  oil7
samayam tamil 
Why should the Oil Preserve be used?
Atthivaradar remained immersed in the water tank for 40 years. His next exteriorization takes place in the year 2059 to grant his devotees his grace and blessings. The idol's body and limbs will rest on the red brick foundation, and the head will rest on a black granite block.  
When Swamy remains underwater, there is a possibility of erosion from the fish and snakes. The idol may erode because of the frequent passing of these life forms in the tank. With the oil preserve protecting the wooden idol, the fish and the snakes will not go near it.  
And the water will cause no damage. During the Placement of Varadar for Sayanam (Divine Sleep) in the temple tank, only a few Archakars of the temple have permission to proceed with his placement.