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 (left to right) Duplex III, Kruss knockoff, GemPro, Duplex II | |
 (bottom to top) Duplex III, Kruss knockoff, GemPro, Duplex II | |
There is an abundance of misinformation about RI liquid toxicity, especially on Internet forums and in outdated literature. This substance requires training and careful handling both by new students and entrenched old-hands. Take a tip from a master: rather than using your finger, manipulate small stones on the stage with a pencil eraser to avoid any possible skin contact with RI liquid (Alan Hodgkinson, 2008). The readings on a refractometer are limited by the RI of the hemicylinder and the RI of the liquid itself. The higher the RI limit of the hemicylinder, the higher the RI of the liquid must be to make use of that limit - unfortunately the toxicity goes up exponentially requiring at least gloves and ventilation, while at its higher limits a lab hood is also mandatory (arsenic salts are used in some formulae). Standard TIR refractometers in use outside of labs usually have a hemicylinder of lead glass with an upper limit RI of 1.90; the highest liquid easily available is 1.81. RI liquid is made from methylene iodide (di-iodomethane) saturated with sulphur giving it an RI of 1.78-1.79. The sulphur alone can cause a bad skin or respiratory reaction in some individuals. Increasing the RI to 1.81 requires the addition of tetraiodoethylene - which is carcinogenic. Alternatively, tin iodide (tin tetraiodide or stannic iodide), a reddish salt, may be dissolved in methylene iodide to increase refractive index above 1.780 in a fashion similar to using sulfur without the addition of tetraiodoethylene (methylene iodide is combined with sulfur up to 1.780 and sulfur and tin iodide up to 1.800). Different manufacturers use different formulae so it is important to know what a particular brand contains and thus what the specific safe handling procedures are. These products, as well as heavy liquids used for SG and immersion techniques, must be used with great caution. It is now recommended by all current literature, gemological schools and laboratories to avoid any skin contact and inhalation of vapors. Some schools have changed to 1.79 RI liquid in light of its lower toxicity. A note on crystal formation and effects of evaporation: when the methylene iodide is allowed to evaporate, the concentration of sulfur or tin iodide is increased thus increasing the refractive index of the solution until a saturated solution forms. More evaporation results in the deposition of crystals of the solids. A tightly closed bottle will not deposit crystals, but you may get some crystals from ones formed when a wetted cap exposed to the air lets the methylene iodide evaporate. These liquids are very dense causing any debris such as crystals to float noticeably on the liquids' surface. Color stability: in sun the fluid will become very dark after one day. When stored in the dark the color is stabilized for up to 5 years by the small piece of copper normally included in the liquid. | |
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