After coating cell culture plates, I leave them to dry in the flowhood (without lid) for about 2-3 hours, then put the plates upside down in a fridge (4 degrees C) inside a closed plastic bag. However, after several days, it seems like there are many tiny small dots on the coating and I have no idea what they are or where they come from. It doesn't seem like there is any moist inside the plate. See first file attachment. Can anyone tell me what this could be, how it happens, whether it affects cell attachment and how I can prevent this from happening?

Another (related) question... my MSc student also recently coated plates and while I thought he did the exact same thing as I did, his coated plates showed an even more interesting pattern... Is this crystallisation of protein? What happened here? (See second attachment)

P.S. plates were coated with a solution of 10 ug/ml fibronectin, 10 ug/ml bovine serum albumin and 30 ug/ml PureCol (bovine collagen).