To have the skill level to carve it in marble.
This sculpture below, " The veiled virgin" is  most impressive. Notice the effect of transparency, from the Italian artist Giovanni Strazza of the nineteenth century.

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Think of the epic difficulty of modelling a veil on a face of a material that is among the toughest on the planet, marble (mineral hardness 3 - Friedrich Mohs scale). Another problem is that marble has nothing added. It is sculpture made by subtracting 100 %. Why say that to sculpt a figure, you take the block and "simply takes everything that is not his figure."

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Other large sculptures that created beautiful marble veils:

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Think of the level of difficulty to carve without breaking it:
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This is a monument to the father of Prince Raimondo Sangro Antonio (1685-1757)
The Italian name of the monument Disinganno is often translated as "disappointment" but not in the conventional sense of it and Church Slavonic - "Freedom of the spell."
"Freedom of the spell" (after 1757 ) of Franschesko Kvirolo and is the most famous of his works, the ability to make this netting.
All made of a single piece of marble and pumice, Kvirolo was the only Neapolitan master who accepted the challenge. Other great sculptors wouldnt, believing that the network would break into pieces.
Amazing master sculptors for centuries the art of precise cutting of the stone.

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How about that texture of skin, Lorenzo Bernini, which depicts the abduction of Persephone? Look
 at the finger pressure on the skin.

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The sculptor was only 23 years old when he made it in 1621. Look at the detail.