Is there a minimum amount of essential oil that one can place on the plate that will provide useful effects?

For molecular scalar, you really don’t need much. Just a small glass dish with even a few drops should work for you. If you want, you can find some glass stopper bottles and put a few milliliters in them, but you probably don’t need an ounce of anything. Then again, it’s YOUR scalar, so do what you feel works. Just touch up the tuning after plunking down a lot of mass on the coil. I don’t find that two or three small glass dishes changes the tuning.

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