I have two identical pieces of glass I found in my house (left by the previous owner). They look like table tops, and measure 22"x22" and are 4mm thick. I was thinking of building a big ferrocell with them. I have been reading on this forum about the importance of glass quality for optimum results and those are obviously not optical glass but they seem in good shape. So my question is would I be wasting my time building a ferrocell with them or do I have a change at achieving decent results.
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.