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GEMMOLOGY > Treatments > Flashcards

Treatments Flashcards

1
Q

Define treatments

A

The process of artificially improving the appearance or properties of gem materials

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2
Q

What is bleaching?

A

The use of chemicals or other agents to lighten or remove the colour of a gemstone. This can cause damage and make the material less durable.

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3
Q

What materials may be bleached?

A

Pearl
coral
jadeite
quartz varieties ie tigers eye

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4
Q

What is foiling?

A

Foil or reflective material is placed behind a stone. Usually found in antique jewellery. Look for crumples

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5
Q

What materials can be dyed?

A

Any that are permeable to some degree ie that has surface reaching cracks or is porous.

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6
Q

How can can you identify when a material has been dyed?

A

A concentration of dye in cracks
The absorption spectrum
The fluorescence may be distinctive
Most organic dyes will stain a swab of acetone - destructive

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7
Q

What is coating?

A

The application of a coloured layer to improve or change the colour of a gem

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8
Q

Give examples of how coating is used in some materials to improve appearence

A
  1. Black paint applied to back of translucent opal or amber to make it look green
  2. Paint the girdle of a yellowish diamond blue
  3. Thin films of compounds of metals eg gold, titanium and cobalt on stones such as quartz, topaz and CZ
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9
Q

What is mystic topaz?

A

Topaz that has been coated to make it look iridescent.

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10
Q

How can you detect when a material has been coated?

A

may see pale lines or patches where scratching or flaking has occurred
Spectrum may show coating of material rather than stone
Can be identified by iridescence effects cased by the thin layers when viewed from the back of a stone

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11
Q

What is a Lechleitner emerald?

A

A synththetic gem coating of hydrothermal emerald on a pale beryl

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12
Q

What stones commonly use impregnation and filling?

A

Turquoise
Jadeite
Lapis Lazuli

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13
Q

Why is impregnation and filling used?

A

To toughen porous or fractured stones

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14
Q

What is stabilisation?

A

Substances such as turquoise, bleached jadeite and soft coral are inpregnated with a polymer resin to provide sufficient durability for wear. The filling substances may also be coloured thus dyeing and consolidating the material in one process

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15
Q

How is jadeite commonly treated?

A

Bleached - to remove dark minerals and iron staining. This weakens it though
Impregnated - resin strengthens and improves the colour and appearence
Dyed - improves the colour

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16
Q

What is B-Jade?

A

When jade is bleached and impregnated

17
Q

What is C-Jade?

A

When jade is bleached, impregnated and dyed

18
Q

What is A-Jade?

A

Untreated jade

19
Q

What does oiling do?

A

Improves the clarity and colour and may suppress the reflections from cracks sufficiently enough to allow the natural colour to display to its full effect

20
Q

Why would an opal be oiled?

A

To disguise the presence of crazing, the fine cracks that appear after the stone has been mined. It can happen with temperature change, loss of water content under adverse heating, lighting or humidity conditions

21
Q

How do you fracture fill an emerald?

A

Fractures are filled with a polymer resin such as Optican. A hardener is then wiped across the surface hardening either all or just the surface of the filling to improve its durability.

22
Q

How can you detect if an emerald is fracture filled?

A

Can be hard to as RI of filler may be close to emerald but may be able to see a flash of light reflected from the filled fracture. Typically it is yellow to orange or blue.
You may also see bubbles, flow structures and cloudy areas in the epoxy filling

23
Q

How do you fracture fill rubies and sapphires?

A

at high temperatures rubies and sapphires may be partially dissolved in a flux called borax. heat treatment in borax can then be used to re-heal some fractures although this may leave a glassy residue. more common in rubies.

24
Q

How can you detect fracture filling in rubies?

A

Look for areas of lower lustre in polished surfaces.

25
Q

How can you detect lead glass filling of rubies?

A

Will flash blue when rotated
may also show orange flashes and bubbles int he filled fracture
A strong lustre difference between the filler and ruby and glass areas will show a poorer polish

26
Q

How do you fracture fill a diamond?

A

Diamonds placed in vacuum chamber or under high pressure to remove air in the fractures and draw the melted glass into them

27
Q

How does heat treatment work in regards to producing, removing or evening-out colour?

A

It changes the chemical state of transition elements by diffusion or by dehydration. Heat treatment resembles processes that occur in nature and is often hard to identify

28
Q

What happens to heat treated Amber?

A

Causes circular stress cracks called sun spangles. These are seen as desirable and is deliberately induced.

29
Q

What evidence is left in heat treated corundum?

A

Disrupted rutile inclusions
stress cracks radiating from crystal inclusions
crystal inclusions may appear whiteish or cloudy
In verneuil synthetic corundum you may see fingerprint inclusions

30
Q

What is prasiolite?

A

Amethyst that has been heated to turn green

31
Q

What is diffusion?

A

Is the alteration of the colour or optical appearance of a stone via colour causing elements from an outside source
SURFACE DIFFUSION - only penetrates the surface of the material
LATTICE DIFFUSION - penetrates deep into the stone

32
Q

How is asterism induced in sapphires and rubies through diffusion?

A

inwardly diffuse titanium

33
Q

How is surface diffusion achieved?

A

Coating the stones with aluminum oxide and the appropriate compounds and subjecting the stones to very high temperatures for several days

34
Q

What are the three types of irradiation treatments?

A

high energy neutron rays produced in a nuclear reactor
Streams of electrons generated by a linear particle accelerator
gamma rays produced by a radioisotope, typically cobalt 60

35
Q

what is annealing?

A

heat treatment thats used to modify the colour produced by irradiation by changing the electronic state of the colouring elements

GEMMOLOGY (5 decks)

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