Pearls (L32)

Question 1

Why is it that edible oyster produced pearls don’t ahve the shone and flow of a nacreous pearl?

Answer 1

b/c edible oysters do not secrete nacre

Question 2

What can make pearls?

Answer 2

any mollusc with a shell

Question 3

the pearls produced by a given mollusc will resemble ____

Answer 3

the interior of its host shell

Question 4

What type of pearls do molluscs that don’t secrete nacre create?

Answer 4

porcelaneous pearls

Question 5

What is the largest known pearl in the world

Answer 5

The Pearl of Puerto which is a giant irregular, porcelanous blister pearl

Question 6

How exatly does a Blister pearl form?

Answer 6

1. an irritant (a parasite) becomes trapped between the shell and the mantle tissue
2. the oyster simply covers over the irritant by nacre secreted by mantle tissue, forming a blister-like growth

Question 7

How does a Nacreous pearl form?

Answer 7

any foreign body that irritates the mantle tissue and cannot be expelled by the mollsuc can form the nucleus of the pearl

the mollusc reduces irritation by surrounding the irritating body with smooth layers of nacre

Question 8

How are Free pearls formed?

Answer 8

less readily than blister pearls

1. a sac has to form that completely surrounds the growing pearl. (in nature, chances of this is very low)
2. forms by the intrusion of a pariste
3. Irritation by the parasite stimulates an infolding of the epithelium (surface shells)
4. the epilethial tissue completely surrounds the paraiste, forming a pearl sac in deeper levels of the mantle
5. when the parasite is completely enveloped and the nacre is secreted on all sides of the invader by the epithelilal cells, free pearls are formed

formed deep within the mantle tissue

Question 9

What happens when the parasite isn’t completely enveloped in the process of free pearl forming?

Answer 9

the secretion of nacre can produce a blister pearl

Question 10

What are the main properties valued in pearls?

Answer 10

these are lustre, body color, and orient

Question 11

What determines the lustre of pearls?

Answer 11

high reflectivity and internal reflection

Question 12

what is the basic color of a pearl mostly dependent on?

Answer 12

Pigments in Conchiolin

Question 13

what else contributes to the light interference that produces iridescence?

Answer 13

the refractive/reflective properties of aragonite layers

Question 14

what is a general rule about the value of pearls?

Answer 14

all other factors being equal, the closer the pearl is to perfectly spherical, the more valuable the pearl will be for a given size

Question 15

What has Perliculture done?

Answer 15

greatly increased the availability of pearls to consumers by manipulating the nacre-secreting abilities of bivalves

Question 16

what are the 3 main advantages of perliculture over harvesting oysters from the wild?

Answer 16

first, it results in a much better pearl count to oyster ratio

second, allows some control over pearl shape

third, it allows some control over pearl size

Question 17

How is the process of growing pearl oysters done?

Answer 17

1. oysters raised in cages or nets to prevent being eaten or damaged and monitor the health
2. once they have grown to a certain size, the oysters are harvested, and the healthiest ones are selected for the critical process of implantation
3. the oysters are anaesthetized so that the oysters relax their adductor muscle and open their shell
4. some pearl oysters (donor oysters) have tehir mantle tissues removed and cut into small strips
5. the mantle tissue is wrapped around a spherical bead and implanted into the recipient oyster’s gonad
6. the gonad heals around the implanted package and forms a sac
7. as the mantle tissue is alive, it will grow around the bead and secrete nacre
8. then pearl is removed when reached prefered size

Question 18

Why is the donor tissue and nucleation bead planted specifically in the gonad?

Answer 18

b/c the key of producing a few pearls is to keep the growing pearls as far away from the mantle of the donor oyster as possible

Question 19

What does the actual pearl size vary according to?

Answer 19

the size of nucleation bead inserted into the oyster

Question 20

How are freshwater pearls cultures a bit differenty than pearl oysters?

Answer 20

the pearls are allowed to grow in the mantle

Question 21

What is a mabe pearl and how is it created?

Answer 21

mabe pearls are technically a blister pearl

and to produce it, hollow, flat-botomed, plsatic domes are inserted in the space between the mantle and nacreous layer of the pearl oyster shell

the oyster secretes nacre on these domes to produce blisters

a year later, the hollow interior of each pearl is filled with wax for support and a disc of mother of pearl is glued to the bottom

Question 22

Where are mabe pearls used?

Answer 22

in peices of jewellery that don’t necessitate a perfectly spherical shape (such as earrings)