Things to Keep in Mind
The smaller the neck on the bottle, the slower the liquid will evaporate. I'm about to learn how much more quickly mine will evaporate with the wider opening of my vase.
Experiment with different essential oil combinations until you find one or two you really like. You can then increase your batches and keep them in sealed containers (like a canning jar) to save prep time later on.
Have any of you made your own diffusers before? Which works better? The oil or the vodka and water? I've love to know!