{"product_id":"untitled-dec-5_22-48","title":"GIA Erb Gray Refractometer (c. Early 1960s)","description":"\u003cp\u003eThis early-model GIA Erb Gray refractometer from the Gemological Institute of America features a turnable hemisphe\u003cimg\u003e\u003cimg\u003e\u003cimg\u003e\u003cimg\u003e\u003cimg\u003e\u003cimg\u003erical prism, mounted on a rotating optical turret. By rotating the hemisphere, the user can perform a 360° refractive Index examination without turning the stone itself - and potentially scratching the soft hemicylinder\/ hemisphere glass. The marking on wheel gives the exact angle the stone turned without guess work.\u003c\/p\u003e\n\u003cp\u003e\u003cbr\u003eThe instrument’s heavy-duty cast housing, textured enamel finish, and flip-up prism cover were designed for protection from damages. A precisely ground hemispherical prism, paired with GIA’s early illumination channel, allowed accurate measurement of refractive indices from common gemstones. Later GIA models has removed this turnable hemisphere and made a cost-effective, more compact designs, this early hemispherical version marks an important developmental step—illustrating how to adapt scientific principles into practical tools that shaped the foundations of modern gemstone testing.\u003c\/p\u003e\n\u003cp\u003eThis is a museum archives and no unit is available for sale at this moment. \u003c\/p\u003e","brand":"Gems.studio","offers":[{"title":"Default Title","offer_id":51333960827200,"sku":null,"price":0.0,"currency_code":"CAD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0963\/0397\/2672\/files\/ErbGray3_1.gif?v=1767233064","url":"https:\/\/gems.studio\/products\/untitled-dec-5_22-48","provider":"Gems.studio","version":"1.0","type":"link"}