I have been stencilling for a while now using screen printing inks. All good, except that these inks are totally opaque, and they don’t blend or flow. So they are not that suitable when you want to do something like this.
Screen printing inks are also expensive. My fibre reactive dyes (Procion, Drimarene K) go a lot further for the same outlay, produce vibrant colours, plus they are transparent if thinly applied and flow into each other for soft transitions. The problem is how to stop them from flowing in an uncontrolled fashion like a drop of ink on blotting paper. To achieve this the dye needs to be thickened with guar gum or some such. I have lots of xanthan on hand, which is a similar seaweed based food grade thickener (very suitable for a seaweed stencil, haha, although it works for everything), so I used this to experiment with.