Block 3 Treatments, synthetics & testing Flashcards
Define treatment
The process of artificially enhancing the appearance or properties of a gemstone
What is the process in sugar-treating an opal?
Opal is soaked in sugar and then dropped in acid to give appearance of a black opal
To identify this treatment look for dark specks in pale matrix
Why is impregnation and filling used as a treatment in porous stones?
It improves stability, colour and clarity
What key features would you look for in a fracture filled emerald?
Mossy inclusion
Yellow flash
filling material may fluoresce
What key features would you look for in a fracture filled corundum?
Blue flash
Bubbles in filled fracture
Iridescence in filled fractures
Change in lustre on the surface
What year was heat treatment first used?
1970
What is the temperature needed to heat treat corundum?
up to about 1900 degrees
How does the amount of oxygen during heating effect the resulting colour of the stone?
Heat + Oxygen = Ferric Fe3+ (yellow) the atom loses an electron
Heat - Oxygen = Ferrous Fe2+ (Blue) The atom gains an electron
If a Zircon is heated in an oxidizing atmosphere what colour will it turn?
White or golden yellow
If a zircon is heated in a reducing atmosphere what colour will it turn?
Blue
If a pale blue sapphire is heated in a reducing (1600-1900 degrees) atmosphere what is happening?
A more intense blue will be produced this is due to the interaction of iron (Fe2+) and titanium.
it will change from Ferric (yellow) to Ferrous (blue)
What happens when you heat a dark blue stone in oxidizing (800-1900 degrees) atmosphere?
Changes from a Ferrous (Fe2+) to a Ferric (Fe3+) and the colour will become paler
If rutile is released in corundum and dissolved by heating to 1750 degrees what is the effect of this?
More transparent stones. Helps to remove silk and stone becomes Ferrous
This is done rapidly
What happens to titanium rich corundum that is heated at slightly lower temp (1100-1400) for 2 weeks?
Improves stars as rutile is titanium oxide
EXSOLVED
What and why is surface diffusion treatment used?
When corundum cannot be enhanced by heating it is embedded in a chemical containing colouring elements and then heated (1600-1750). However only penetrates stone to a shallow depth.
Can be seen when stone is immersed and the colour distribution will follow the facets
What is lattice diffusion?
When the material is heated in the presence of another material ie beryllium.
This treatment can penetrate much deeper than surface diffusion
What is irradiation?
Bombardment with either atomic particles (diamond) or gamma rays (most other stones).
It is used to change the colour of a stone and can either be permanent or temporary
If a greenish blue aquamarine is heat treated what colour will it go?
Blue - as needs higher concentration of of ferrous ions
If greenish blue aquamarine is irradiated what colour will it go?
Yellow - Needs higher concentration of ferric ions
What does irradiating a diamond do?
Displaces carbon atoms
What does HPHT treatment do to diamonds
Heating to above 2000 degrees can alter the colour
Brown to grey type 11a (no nitrogen) become lighter in colour
Nitrogen bearing stones become yellow to to green with strong fluorescence
If they contain boron they become blue
In synthetic production of gemstones what does cyrstallisation involve
Nucleation and crystal growth
Explain what nucleation is in crystallisation
Occurs when atoms come together in the correct orientation
seed crystals are usually provided to take the place of nuclei
Explain what crystal growth is
Atoms join the seed or nucleus to forma regular structure
