These air bubbles usually occur if too much xylene is left on the slides.
As the slides dry the xylene evaporates and leaves the air pockets

> ----------
> From: 	Fredrickson, Michael M.[SMTP:MFREDRICKSON@PARTNERS.ORG]
> Sent: 	Tuesday, April 04, 2000 9:50 AM
> To: 	'Levac Caron, Joelle'; 'histonet@pathology.swmed.edu'
> Subject: 	RE: Leica coverslipper
> 
> Yes, we have encountered this strange problem.
> 
> We are using xylene on the stainer and Polymount from PolyScientific on
> the
> CV5000.   I have adjusted the mountant type from "1" to "2" and left the
> volume setting at approximately "2". We also ensure that the slides have
> not
> dried before placing them on the coverslipper.  
> 
>  I have been using these settings for the past month with an apparent
> decrease in this bubble phenomenon.  
> 
> -----Original Message-----
> From: Levac Caron, Joelle [mailto:jlcaron@Ottawahospital.on.ca]
> Sent: Monday, April 03, 2000 3:57 PM
> To: 'histonet@pathology.swmed.edu'
> Subject: Leica coverslipper
> 
> 
> Hi
> Has anyone encountered "bubbles" or "voids" on slides after  a 2-week
> storage??  A  Leica CV5000 coverslipper was used to mount slides.
> Which clearing agent and mounting medium are you using??
> Joelle
>