I want to know what they're usually made out of? The one I have at home is made out of porcelain.

When did they first start showing up? When did the modern statues (Painted) begin to show up?

'pray_pray'

Do we need to "kai guang" statues before offering worship?

What is the effects of not doing so and with sincerity, requests the deities to bless the statues by oneself without the intervention of taoist priest?

Can the statues be clean regularly?

Thanks
Chow

In certain Religious beliefs, yes, a statue needed to be "Kai Guang", reasons:

1) To invite the main source of the energy from the Deities that the statues belong too, in-order to "receive" the communication from the human.

2) Upon inviting the positive energy from the Deities, then the "empty" statues wont be "possessed" by negative energy which later would cause harms to the ppl worshipping.

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Kai Guang ritual/ceremony not necessary to get involved with very physical actions like doing dotting on the statues or using burning joss-paper to go round the statue body, some other methods are like:

1) by reciting the Invitation Mantra for indivdual Deity

2) by allowing the statues to stay in temples for certain number of days to allow them to absorb the postive energy

Again, sincerity is the most important.

Some ppl can go without doing anything to the statue and yet they are being blessed by the particular deity.

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Regularly cleaning is encouraged but in the way of not disturbing or moving the statue or urn.

For some Masters, they advised that on the altar, it must always kept clean and dust-free, this goes the same to the statue.