Dear Dirk,

I suggest for you a links and attached files in topics.

-Crystallography for beginners – part 5 – monitoring and evaluating ...

https://benchwise.wordpress.com/.../crystallography-for-beginners-...

-X-tal protocols: Description of what you see in the drop.

www.xtal-protocols.de/drop/drops.html

Best regards

Make sure your protein is pure and in high concentration.  Test them for purity and concentration.  Only after making sure that the protein is pure and in high concentration will I try crystallization.  In the crystallization, use commercially available crystallization kits (as they are standardized) instead of making up your own solutions. Store the crystallization set-ups in environments that are vibration-free.  

Thank you all for your answers.

The clusters are usually small, the size of a small-medium sized crystal and some of them are pretty dark or brown. I can make some pictures on Monday and upload them but I also read somewhere else that this is a bad sign and usually doesn't result in crystals. So maybe I should go into another direction.

I got this condition from a screen and thought that my protein is pure enough. I just see some minor contaminations on the SDS-PAGE gel at high protein concentrations but of course it could always be purer.

And Terese won't unfortunately be back in the lab before February :(.

I found another drop which contains gel (at least I think it's gel). Apparently that is a good sign but I'm not sure what the best way to continue with this one is. I attached a picture of this drop.

Brown can be an indication of denatured protein, if they are crystalline clusters you may have a starting point to optimise from.

The drop you have supplied a picture of is phase separation, to be honest I've never considered this kind as a drop to follow up. I generally look for crystalline precipitates and clear precipitates.

Definitely agree with Cornelius do not reinvent the wheel, have a chat with Terese Bergfors or one of her group. Also buy her book  "Protein Crystallization" or get it from the library!

I checked the "cluster"-plates again today and took 2 pictures (which I added to this answer). Now it looks like something grew in the clusters. It looks like phase separation or maybe spherulites under the microscope.

So what's your opinion on these?

Thanks for all the help!

Top one crystalline bottom looks like  crystals, worth mounting and shooting to see if you get diffraction.,

Besides the protein, what else is in your droplet?  Are there salt(s) in them? The tiny crystallites you showed look like salt crystals to me.  Try adding a small amount of dye (e.g., Coomassie blue) and see if the crystals take up the dye.  Protein crystals will take up the dye (because they have larger spaces or interstices within the crystal lattice), while salt crystals will not.