My experiments have led to one unforgettable/unforgivable disaster:
What I am looking to create is an oilspot or hare fur effect (like on the inside of the bowl above) where the iron will really work its magic and separate into many colours when it starts running. I want to reduce the metallic sheen. And I want it to stop running so much and ruining my kiln furniture!
It is a tall order.
Recently I think I may be onto something. In my next test I will lower the bone ash and iron content and replace some of the talc with magnesium. We shall see if the kiln gods are with me next time.