[Histonet] Immuno Artifact?

[jason m]

Can anyone identify the cause of this black circle artifact? It is small 
black circles that look sort of like air bubbles only much too small which 
have been turning up on my immuno's this week. I have changed all solutions 
but still have the problem. Our lab uses toluene instead of xylenes, I am 
wondering if that is the problem. Also I use Tween-20 in my citrate buffer 
and I wonder if that could be the problem. At any rate I will be checking 
both of these but if anyone can help It will be appreciated immensely. I 
have sent a photograph of the artifact to the the list serv image archive 
(see link below) under the filename "artifact.jpg".

http://www.histonet.org/site_images_frame.asp

Thanks again,
Jason