In our first shot, we are having a glass of water be turned a colour (most likely red) by a pill or droplet. We then want the water to turn clear again. We asked the chemistry department if there was a chemical that could do this and they told us of such a one (the name has escaped me). However we are yet to enquire if they have that chemical and if they would perform the experiment; so we could film it.
An idea for a second solution to this shot is that we could use a drop of red food dye to film the water turn completely red. We would then film it again; making sure the camera hasn’t moved and the glass (with new clear water in it) is in the exact same place. In editing we would then slightly crop both shots to make sure they are both perfectly identical, then we would reverse the second shot. The result would be a sequence where the water in the glass turns red and then turns clear again. It would not involve the chemistry department performing an experiment for us and would not need a peculiar chemical.