Your portrait came out just great!

I just saw your question and thought you might be interested in this email response from WN. Last month I emailed them and asked about the fat/lean rule when using fast dry medium and this was their response:

The Fast Drying Medium is considered ‘Fat’ so you shouldn’t have any problems. The ‘lean’ materials in the Water Mixable Range would be the Artisan Thinner and water. They don’t offer any adhesive or binding properties.
When it comes to fat over lean……………what that really means is ‘more flexible over less flexible’…………….Mediums are fat so increase the flexibility. What you don’t want to do is to apply a layer of oil colour mixed with either water or thinner over a layer where you have used only medium. The ‘lean’ layer will dry quicker and slow down the drying of the under layers. It will become more brittle than the paint under it so when that layer dries is likely that the ‘lean’ layer will crack.

i just read somewhere, that the WN oil thinner and linseed oil can be added to the fast drying medium without adversely effecting it.

same here, I don’t use the WN water mixable mediums, I use regular mediums, liquin, OMS, linseed oil. Many claim that this will make them not water mixable, but for me they are still water mixable because most of the material is the WMO paint and not the medium.

I too struggle with what quantity and at what stage to mix artisan fast drying medium. I have been for a few lessons whereby the teacher scrubs the first layer of paint into the canvas using very little paint, so consequently you can carry on painting on top immediately doesn’t use any mediums. So I don’t really know the proper way to use my fast drying medium. Would like to see a demo of a landscape from start to finish using the medium, as some of my paints seem a little dry to work with (a bit like acrylics)