Avoid Scratching the Prism
The measuring prism in many refractometers is constructed out of soft glass that is easily scratched. Be careful not to touch the glass with any hard and/or sharp object, such as a pipet tip or metal spatula. Never rub the measuring prism.
Clean the Prism Immediately After Use
Use a wetted tissue or cotton ball for cleaning the prism glass and use a dabbing motion rather than a rubbing motion to minimize the chance of scratching the prism. Good choices as cleaning solvents are ethanol or isopropanol since they are inexpensive, relatively nontoxic, and won't degrade the prism seal. If aqueous solutions are being measured, the refractometer may be cleaned with distilled water, possibly containing a small amount of nonionic detergent if necessary.
Avoid Solvents That Degrade the Prism Sealant
The sealer around the prism may be degraded by certain solvents. For example, the Bausch & Lomb Abbe' Refractometer should not be used with the following solvents:
Acetic Acid Solutions
Other solvents may degrade the sealer at slower rates and should not be used as the normal cleaning solvent:
Avoid Strong Acids or Bases
Strong acids and bases will etch the prism glass.