NVH Oil is a very high viscosity oil suitable for room and variable-temperature diffraction measurements. Crystal motion during data collection is minimized, even when thick layers are used to prevent dehydration.
This oil is very effective in removing external solvent to prevent ice ring formation during cooling. Move your crystal back and forth in the oil, transfer to fresh oil, and repeat until you no longer see solvent trails and the crystal becomes nearly invisible.
Many protein crystals prepared in this way can be slowly cooled to 100 K without appreciable degradation of diffraction properties, allowing data collection at arbitrary temperatures. Unlike Paratone-N oil, this oil does not form diffraction rings when cooled.