I do not have access to Geneva paint. I use schmincke Norma professional with Mark Carders medium recipe. Or should I say have everything ready to go but yet to mix the colours. I have the mediums made but one thing that Mark Carder does not mention is how to add medium to black paint. His tutorials where made before he sold a black paint, so would expect people to blend a blue/brown black. So, I have an Ivory black, do I add normal colour medium, or add extra clove oil?