Thanks for point out this link (or was it Loris in the original post). I never made it that far and it made for a very interesting reading.
One thing that Bruce MacEvoy mentions is yupo for one of the experiments and explains why watercolors look very luminous on that substrate. It totally agrees with my observations and has reignited my desire to experiment some more with yupo. I have some nice prints and they just glow. Main problem with it is that gum does not stick to it and it seems to be unpredictable in the way it peels off and flakes. Sometimes patches will come off, sometimes just spots.
Here are some prints
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