I have never used anything other than plain water, boiled for around 1 hour + or - depending on the thickness. That is the same way I make them soft for forming a round plug also. Some will say to use oil in a fryer, but you better know what you are doing or you will cook it and then they become brittle and will break like glass. I have been working horn for 8 years and never used anything but water. Good luck and have fun with it.