Structural Medicine     

Protein Crystallography Course


Terese Bergfors' Pictorial library of crystallization drop phenomena
Johan Zeelen's X-tal Protocols crystallization drop phenomena

Look at your drops using the polarizer on the microscope under the highest magnification.
Crystalline objects are "glinty" and have birefringence, changing colour as you rotate the polarizer.

For an excellent explanation of birefringence with java applets see the site on Optical Birefringence by Molecular Expressions.

There are 9 possible things you will see, possibly in combination (photos used with permission as credited).

If you see a crystal...
Is it salt or is it protein?

There is no reliable way to tell if your crystals are salt or protein except by collecting an oscillation image (see section on shooting). But you can try:

If you see a crystal a year or two later...

If you see a crystal, don't go running down the corridor screaming "EUREKA!!!" until... . .
. you know your crystal isn't salt... and that it diffracts.

© 1999-2005 Airlie J McCoy, University of Cambridge. All rights reserved.

Last updated: 7 June, 2005