I had a lot of fun making these a few days ago with a dear chum.
Instructions from here-
I actually used sachets of plain gelatine crystals rather than sheets and I would be interested to hear if they work with the vegetarian equivalent of gelatine. Knowing what I know now, I would use smaller jars and I found the two I made using food gel colouring rather than the traditional food colouring were more effective- the green one made with the latter has all the attractive look about it of a jar of pond water, although it smells nice. I don't buy gel air fresheners because I don't want the leftover unrecyclable container to deal with and this seems to be a good alternative.