Micro Kristal Klear can do so many things that can make a big difference in the appearance of your models.
First, Micro Kristal Klear is a liquid that can be used to form very real looking small windows up to about 1/4 in size.
It is also an adhesive for mounting clear plastic parts, windows, etc. on models.

Microscale Instruction Sheet: http://www.microscale.com/Merchant2/graphics/Instructions/MSISysteminstr.pdf