iBooks embedded fonts

I am building a family cookbook in an epub using Sigil and Calibre. I have embedded a special font for some headings. In all views; Sigil, Calibre, and iBooks on the MacBook I see the fonts properly. When I move the book to my iPad the embedded fonts don't work, everything displays in the default font. Does the iPad have some special codes needed in the css or a setting I'm missing in settings?