Table 1. Summary of the major observation techniques for identifying crystals and following the crystallization process.

Technique	Spatial resolution achieved	Time	Expense	Outcome
Eye	∼500 µm	Rapid	None	Identification of the presence and position of large crystals. Measurement of number and size.
Visual microscopy	∼2 µm	Rapid	Low	Identification of the presence and position of large and small crystals. Measurement of number and size
UV microscopy	∼2 µm	Medium	Medium	Identification of the presence and position of large and small crystals. Measurement of number and size. Distinguishes between biological and salt crystals in many cases.
Light scattering	A few nanometres	Medium	Medium	Characterization of size distribution. No number or positional information.
SONICC	∼0.2 µm	Medium	High	Identification of the presence and position of large to nanocrystals. Measurement of number and size. With TP-UV, distinguishes between biological and salt crystals
Electron microscopy	50–100 Å, (individual proteins) ∼5–10 µm	Long	Very high	Identification of the presence and position of large to nanocrystals. Measurement of number and size. Distinguishes between macromolecular and salt crystals. Characterization of diffraction quality.