Oil paint is just pigment mixed with linseed oil,,its not modern,, it can be toned down to look ancient,
or glazed over to look older or for more natural look, as suggested the dyes and hull tea,,
there are many ways to achieve the look you want,, even modern acrylic can be diluted and toned down to have a more ancient look,, even watercolor can be used to look natural,,
if you showed me a picture of what you want to achieve,, I could give you a more definitive suggestion,,
