For use with all gemological refractometers. Gem-Master 1.81 Refractive Index Liquid is bottled in 5ml amber glass bottles, each containing 3.2mls of liquid. Each bottle is fitted with a Teflon “restrictor” neck-insert which forms an airtight seal with the cap, limits the amount of liquid withdrawn at a time, reduces the emission of harmful vapor (70% less than a standard open-necked bottle), minimizes spillage, and prevents accidental ingestion.