I am a Potter and I make oil warmers in stoneware. Several years ago I tested a bunch of oil mixtures to be able to sell along side my oil warmers. Nothing worked for me. I used DPG and fragrance oil, I used carrier oils, even mineral oil. The tealights heated the mixture and the smell from the oils overpowered any essential or fragrance oil I used. I tried commercial mixtures and had the same experiences.
I was moaning and *****ing about my issues to a friend from Australia and he told me that at work they routinely use a tealight oil warmer with eucalyptus oil when anyone is feeling congested. He said that they just put water in the top with a few drops of essential oil and kept the water topped off so it didn't' run dry. Just like navigator mentioned above.
I now easily sell my oil warmers by telling people they can simply use water in the top with their favorite essential oils and it is gentle enough to use on a desk top, but very often the scent carries lightly through a room. I also feel it's the best way to diffuse essential oils to keep them at their best scent carriage and not to try to burn them in a candle...which presents its own issues.
...I also sell tealights with smaller wicks just for oil warmers. They burn a little longer than my usual tealights and work beautifully for these.
