How do refractometers work?

Refractometers use a transmission type optical measuring system, which allows light to pass through a liquid. According the refraction phenomena arising at the interface with the prism, it splits cleanly, forming a boundary line on the scale face. The scale is read in terms of the position of the boundary line. The dark side of this boundary line is designed to appear as sharp blue. For this reason, taking readings has become easier, even with dark coloured or extremely cloudy liquids.

Refractometers have the broadest range of applications. Lightweight and easy to use, they require only a drop or two of liquid to give an instant reading. The equipping of most models with rubber grips and rubber boots has had the effect of further stabilizing measurements. The transmission of hand heat to the refractometer has been rendered difficult and temperature error greatly diminished.