I am making soya candles with essential oils. After burning for 30
minutes why does the flame start to be unsettled and flickering non
stop?

The wick could be to thin or of poor quality, does the top of the
candle looks concave after it has been burning for a while?

The wick is square cotton braided no.2. The diam. of the container is
approximately 2". The top layer of the wax becomes liquid and then the
wick is flickering all the time.

some of the less expensive oilds do not fully defuse into the wax and
only the outer layer of wax has enougf oil to be smeled. that combined
with the fact that the olfactry sences start to hibuate afrer 20 to 30
min you have to have a stronger sent for it to smell as strong at
first. about the flickering i would presoom that the wick is to blame
try using a difrent wick manufacture and see if that helps
good luck