I think one trick for this is to make sure that you keep the wick short on the top. This works especially well if you don't leave your lamp lit 24 hours a day. The longer the wick (above the cork), the bigger "briquet" that will form.
This is what I do. I use the wicks shown in the photo (Greek wicks and float)
and what you say Deacon Anthony is the trick. I have a small lamp container however it goes often more than a day (it depends though). I will just light a new one now and I will report how much oil is in the container that I have and also for how long it stayed on.
Wow, Robert, Olga is right that what you say is so interesting.
Another question for all: how do you dispose of the wicks and other things remaining from the oil lamp and the censer? I have a large vase with a palm and I place there what remains of the wicks and the charcoal from the censer. and overturn the earth time after time. Needless to say that is one of the best and lush plants I have and while I re-pot all my flowers, that palm has never been re-poted.
I place the glass lamp container in the dishwasher (I have a couple) when the oil in it is finished. What Robert wrote made me think: Should I wash it by hand? I just think that the high temp. in the dishwasher is better to wash the oil. Also do you first rinse it with water and throw it in a special place and then wash the lamp?