View previous topic :: View next topic |
Author |
Message |
daviddillman
Joined: 04 Dec 2010
Posts: 51
Location: Texas
|
Posted: Dec 28, 2011 21:37 Post subject: Detecting Filling with Polymers |
|
|
What is the best way to determine if some sort of polymer has been used to "fill" cracks or repair other defects in a specimen. I am specifically interested in beryl crystals. I looked at a good sized red beryl at a show this year and I asked the dealer about this. His answer was something on the lines of "..I looked at it and I don't think so... Not very reassuring. What tests can be done? Thanks. _________________ DSD |
|
Back to top |
|
|
gemlover
Joined: 31 Dec 2008
Posts: 211
Location: Easley, SC
|
Posted: Dec 28, 2011 22:25 Post subject: Re: Detecting Filling with Polymers |
|
|
There is not enough room here to totally discuss how to detect filled fractures and other features in gemstones. Many fillings can be seen with careful examination of the stone with a loupe. Some require much more sophisticated equipment. I refer you to the journal "Gems and Gemology" published by the Gemological Institute of America for many articles regarding this. Unfortunately, many of the dealers at shows have little or no knowledge of gemology.
John _________________ John
John Atwell Rasmussen, Ph.D.. AJP
Geologist and Gemologist |
|
Back to top |
|
|
gemlover
Joined: 31 Dec 2008
Posts: 211
Location: Easley, SC
|
Posted: Dec 28, 2011 22:29 Post subject: Re: Detecting Filling with Polymers |
|
|
Additional, that I forgot to include:
https://www.gemologyonline.com
(link normalized by FMF)
There is a forum with this group that discusses filling and other gemological issues.
John _________________ John
John Atwell Rasmussen, Ph.D.. AJP
Geologist and Gemologist |
|
Back to top |
|
|
cascaillou
Joined: 27 Nov 2011
Posts: 250
|
Posted: Jan 06, 2012 12:24 Post subject: Re: Detecting Filling with Polymers |
|
|
Fracture filling with colorless oil, polymer resin or glass of close refractive index will improve clarity of the stone (fractures become invisible).
Fracture filling with coloured oil/resin/glass can also improve color at the same time.
Porous stones (jade for instance) can also be impregnated with oil or resin (the stone being porous, fractures aren't required to permeate the stone), which will improve transluscency (as well as color if the oil or resin is coloured).
Fracture filling (or impregnation of porous stones) with oil or resin involves applying light heat and pressure so the oil or resin penetrates deep into the fractures of the stone.
Fracture filling with glass involves stronger heating and thus isn't used in heat sensitive stones (such as emerald).
Oil or resin can be applied to both rough and faceted stones. Glass filling could apply to rough, but is more likely to be encountered in faceted stones.
Oil and resin treatments aren't very stable: the oils will eventually dry and turn yellowish or possibly opacify, with time similar problem can be encountered with resins, moreover resin infusion can fragilize the stone (especially emerald) as resins do expand during drying.
Glass-filling is more stable but could still be damaged by jewellery repair processes involving heat, boiling in acids, repolishing.
Fracture filling and impregnation treatments should be disclosed by the seller.
Oil or resin treatments can be detected under magnification:
-one might watch for partially filled fractures, possibly air bubbles stuck in the filling material (watch the stone in transmitted light), or sometimes flowing aspect in the filler material.
-when the filler is coloured, one might observe color concentration along fractures (or between grain boudaries in the case of stones of grainy structure)
-there can be a waxy/greasy look to the stone, with syrup like appearance inside the stone
-fillers can leak out from the fractures at the surface of the stone
-there can be reflectance disruption on the filled fractures at the surface of the stone (use incident lighting)
-there can be 'colored flash effect' inside the stone (which is seen in grazing light or darkfield lighting). Note that irridescent rainbow-like interference colors on fractures must not be mistaken for flash effect.
-contrast under UV light (as there could be a difference in fluorescence between the filler and the host stone revealing the filler material)
-rubbing with acetone might dissolve some of the filler (which might reveal it)
-immersion of the stone in a liquid of close refractive index helps with observations under magnification, also try observation between crossed polars under the microscope.
-at last, for decorative stones (not for emerald!) one could use the hot needle test to detect resins/polymers.
note: advice number 1, 5, 6, 7 and 9 also apply to detection of glass-filled stones
Laboratory detection: infrared sprectrometry (ftir) and/or Raman spectrometry is used for detection of oils, waxes and resins. |
|
Back to top |
|
|
|