Ways of installing various types of idols
The following has been taken from Varaha Purana. Varaha purana has been explained by Swayam Bhagavan Varaha Swamy to his beloved wife Prithvi or BhooDevi.
IDOL MADE OF WOOD
This swastika mark must be carved out on the idol. Similarly, other signs of Lord Vishnu like 'srivatsa' and 'kaushtubha' should also be carved out on the idol. Lord Vishnu is then invoked and requested to dwell within that idol by chanting mantras. After the deity has been invoked, the 'wood' no longer remains a lifeless structure but it becomes the embodiment of the deity. The idol is then considered to be fit for worship. While worshipping, a devotee should offer a bhoga of kheer to the deity. Burning a ghee or sesame-oil lamp in front of the deity is considered good. The devotee should then circumambulate around the temple premise. While circumambulating, he should keep on chanting the sacred mantra 'om namo narayanaya'. The idol thus installed should be worshipped daily without failure."
"A proficient sculptor should be chosen to carve out the deity's shape from a pure and spotless stone. First of all the sculptor should clearly draw the outline of deity's appearance on the stone with a marker and then carefully carve it out from the stone. The idol is then purified by sprinkling 'akshata' on the deity's idol. While worshipping a devotee should burn a ghee lamp and invoke Lord Vishnu to dwell in that idol by chanting the sacred mantra-om namo narayanaya. The installation of idol being complete, he should observe a fast for the whole night. Next morning, after finishing his daily chores he should put on white clothes and change his old 'yagyopavita' with a new one. The idol thus made is considered fit to be worshipped. Purva-bhadrapada is considered to be the best time for the installation of a stone-idol. During the course of installation ceremony, a devotee should live either on milk or cereal like barley. The rituals of worship consist of numerous activities like lighting four lamps in front of the deity, keeping four small pots each filled up with articles like 'panchagavya', water, sandalwood and milk. The rituals of worship are considered to be incomplete without the chantings of vedic mantras."
EARTHEN AND COPPER IDOLS
A devotee should carefully make a beautiful earthen idol without any sign of crack. The most auspicious time for the installation of an earthen idol is said to be during 'shravana nakshatra'. An invocation is made to the deity to dwell within the idol after which ablution of the idol is performed with the help of various articles like holy water, panchagavya, sandalwood, etc. The rituals of worship are similar to that of woodden or stone-idol."
"The best time for the installation of copper idol is said to be during 'chitra' nakshatra. The idol should be installed facing north and should be purified with the help of holy water, panchagavya, etc. Then the deity is invoked to dwell within the idol. The invocation is made by chanting sacred mantras. Now, the idol is fit to be worshipped. The rituals are same as mentioned earlier."
"The most auspicious time for the installation of bronze-idol is said to be during jyeshtha nakshatra. The idol should be installed facing north. At the time of installation the devotee must not forget to keep four small pots in front of the deity, each filled with articles like 'panchgavya' water, sandalwood and honey. The rituals of invocation as well as worship are same as mentioned earlier."
SILVER AND GOLD IDOLS
"The rituals for the installation of silver or gold idols are similar to that of copper or bronze idol. Prithvi requested Lord Varaha to reveal the name of deities whom a devotee can worship at home. Lord Vishnu replied - "A devotee can worship any deity at home but worship of two Shiva Lingas is prohibited. Similarly, a devotee should never worship three Shaligramas or three Durga idols or two Surya idols. A devotee should also never worship Shaligramas adding up to odd numbers – 3, 5, 7, etc. But, there is no harm in worshipping one Shaligrama. A devotee must never worship broken or cracked idol because it does not bode well for the worshipper. A 'chakra' mark on the Shaligram is considered as very auspicious and it can be worshipped even if the idol is broken or cracked. The virtues attained by worshipping twelve Shaligramas are similar to that of worshipping twelve crore Shiva Lingas. Partaking of 'charanamrita' that has been offered to Shaligrama absolves a man from all his sins. But, a devotee should never partake any 'prasada' that has been offered to Shiva Linga. Anybody who either buys or sells a Shaligram is certain to go to hell."
OM NAMO NARAYANAYA