I've tried these two different ways and I think the silicone mold is the way to go.
What you will need:
Essential Oils: Just about any combo will work - I did Peppermint - for sinuses, Thieves - colds, Lemon or a Citrus - wake up call, Lavender - Bedtime
Glass Bowl - a must with oils
Mix 1 c baking soda with 1 T cornstarch and about 1/3c water - add slowly - until it forms a slightly pourable paste - not runny. I found I had to keep it moving - if too runny the baking soda settles on the bottom of the bowl. Fill mold 1/4 full - the picture below is WAY too full - see next photo for mess:
They boil over when a little watery and over full - but still pop out of the mold really easier than using a baking tin and papers (I popped the pieces off the edges and put them in a bag, added oils and sprinkled in the shower.)
Bake at 350 for 20 minute or so. Let cool. Add your choice of oils - about 7-8 drops total needed. You can store in a glass jar if all the same oils. I gave them out in sealed sandwich bags.
Here is baking tin and papers: the papers were wet when I took them out of the oven and when they dried I couldn't get the paper off the disc. Had to put the whole thing in the shower and retrieve paper from the drain.
Put these shower discs in the bottom of your shower where the water will hit it gently. The oils will rise up and fill the shower! You can also use these in a material bag and put in your dresser drawer with Purification to keep your clothes smelling great!