Requesting opinions on custom project

Big glass must be perfectly flat or you will end up with dark patches and light patches of fluid instead of an evenly dispersed layer.
A simple test would be to mix some red (or other bright color) food coloring with a few ml of water. Clean one surface of each plate of glass. Lay one plate flat. Pour the colored water on to the center of the plate. Slowly lower the second piece of glass (clean side down) onto the other plate. If the glass plates are perfectly flat, you will be able to remove all (if any) of the bubbles and end up with a sheet of colored glass.
You can easily clean the glass plates and use them again.

If you can't smooth out all of the bubbles, they won't work with ferrofluid, either.