Recipe for making a wax that is very hard as a coating for the horn.
Melt 50% bees wax and 50% candle wax in a pan over water. Get rosin and melt this into the wax mixture (the rosin might need a blow touch on low setting to melt it) about 1 cm cubed per half pint of wax. Pour the wax into the horn, swill it about and pour out the contents (remember to keep the wax melted). Keeping going to build up progressive layers. As far as I am aware, the rosin is only "hazardous" in gas form, so be carefull when heating.
I saw this method used to make moulds of apples and fish.
I hope this makes sense!!!!!