Treatments Flashcards
Define treatments
The process of artificially improving the appearance or properties of gem materials
What is bleaching?
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.
What materials may be bleached?
Pearl
coral
jadeite
quartz varieties ie tigers eye
What is foiling?
Foil or reflective material is placed behind a stone. Usually found in antique jewellery. Look for crumples
What materials can be dyed?
Any that are permeable to some degree ie that has surface reaching cracks or is porous.
How can can you identify when a material has been dyed?
A concentration of dye in cracks
The absorption spectrum
The fluorescence may be distinctive
Most organic dyes will stain a swab of acetone - destructive
What is coating?
The application of a coloured layer to improve or change the colour of a gem
Give examples of how coating is used in some materials to improve appearence
- Black paint applied to back of translucent opal or amber to make it look green
- Paint the girdle of a yellowish diamond blue
- Thin films of compounds of metals eg gold, titanium and cobalt on stones such as quartz, topaz and CZ
What is mystic topaz?
Topaz that has been coated to make it look iridescent.
How can you detect when a material has been coated?
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
What is a Lechleitner emerald?
A synththetic gem coating of hydrothermal emerald on a pale beryl
What stones commonly use impregnation and filling?
Turquoise
Jadeite
Lapis Lazuli
Why is impregnation and filling used?
To toughen porous or fractured stones
What is stabilisation?
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
How is jadeite commonly treated?
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
What is B-Jade?
When jade is bleached and impregnated
What is C-Jade?
When jade is bleached, impregnated and dyed
What is A-Jade?
Untreated jade
What does oiling do?
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
Why would an opal be oiled?
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
How do you fracture fill an emerald?
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.
How can you detect if an emerald is fracture filled?
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
How do you fracture fill rubies and sapphires?
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.
How can you detect fracture filling in rubies?
Look for areas of lower lustre in polished surfaces.