Crazy idea! Medieval style paint for icons, painting idea.

I have been doing research into Christian art and Medieval church decoration for a few years now my favourite period is the late 16th/early 17th century. When you get all the macabre art, The dance macabre, laughing skulls and kissing corpses but recently I have been looking at 13-14th century art, its really naïve and kind of lends itself to being painted small on shields and icons.

Medieval artists were somewhat limited in pigments and materials. Oil paints were available/could be produced at home but were very expensive due to the cost of oil extraction. The most common media used would have been tempura due to the availability of eggs and relative ease of production.

So I'm wondering about all my icon shields and paintings for my procession warband being painted with tempura to give it a real stolen from a medieval rural church vibe. It doesn't really matter about waterproofness and fastness etc because I use varnishes and it would give the paint the right visual texture.