interaction between black soap and essential oils

hi everyone,
 trying to introduce  essential oils in black soap such as eucalyptus and rosemary essential oils I found that it  liquified and separated after a month or a little bit more so 
 to preserve it longer than that is impossible.
black soap is just a simple saponification of olive oil with potassium hydroxide and the mixture is heated at 65C for 3 hours when it is completely cooled i add essential oils   proportions ranging from 0.5% to 2% according to the request of the customers and put in pot and costumers ask me to do something so that it can last longer.
 I would like to know if anyone has an idea about  the cause of this separation and liquification I think to saponify the olive oil with a mixture of the hydroxide of 10% sodium potassium hydroxide 90% what do think?
black soap is a pasty soap used for centuries in north africa for scrubbing skin while having bath 
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