Well, isn't that nice, I drop in here and what do I see, my painting
Friend Carol I am honored that you thhought this was good enough to use as an example.
Ian, this is one heck of a beautiful photo!!!!! Sure hope you can pull it off, it would be worthy of a magazine!!!!
My advice would be to wet the desired area, let the water sink in and then drop in your colour; do this over and over again. i.e. let's pretend you are painting the tea pot, prewet the WHOLE area each time, as long as the paper isn't too wet the new colour will float into the area and not leave any sharp edges because once you have a few coats of paint on there it will be near impossible to soften the edges without adversely affecting the previous coat.
Even when prewetting after a few glazes are already in there, be creful not to lift pevious colour, as one of my friends used to say, just let the wet brush gently kiss the paper