{"product_id":"gia-erb-gray-refractometer-c-1960s","title":"GIA Erb Gray Refractometer (c. Later 1960s)","description":"\u003cp\u003eThis later-model GIA Erb Gray refractometer from the Gemological Institute of America features a fixed hemicylinder prism. With this fixed version, the user can perform a 360° refractive Index examination only by turning the stone him\/herself - and potentially scratching the soft hemicylinder\/ hemisphere glass. \u003c\/p\u003e\n\u003cp\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":51335551516992,"sku":null,"price":0.0,"currency_code":"CAD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0963\/0397\/2672\/files\/ErbGray2_1.gif?v=1767233165","url":"https:\/\/gems.studio\/products\/gia-erb-gray-refractometer-c-1960s","provider":"Gems.studio","version":"1.0","type":"link"}