Small holes and blisters on the surface are quite common, but ordinarily they are scarcely perceptible to the naked eye.
Many
faults can be concealed by the jeweller when the pearl is mounted.
Slightly buttoned pearls are set on a peg in the centre of a small
shallow cup; they then appear quite round. A spot, blister, or cavity,
in a round pearl can be obliterated by pegging, or hidden in the
setting. Great irregularities in the sphericity are lost to the eye
when the gem is set in the prongs of a ring or other piece of jewelry.
Pearls shaped like a double convex lens may be made to look round, or
very nearly so, by piercing them so that the flattened domes are
brought in contact on the cord holding them together as a necklace.
Piercing
and stringing obliterates or hides many flaws. By careful selection,
the jeweller can utilize pearls having a blemish by drilling through
the spot where the flaw is, and if there is another on the opposite
side that also will disappear. Other imperfections near the hole are
often hidden in necklaces, as they cannot be seen when the pearls are
held close together
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