Having liked the results written up in my post, experiments with plastic, I decided to try different combinations of black and bright colours.
Black gesso and black acrylic under brights (magenta vermillion and cadmium yellow medium).
Black acrylic and India ink as the top layer over the bright colours.
In each case (black under/black over) I used the medium at full viscosity or watered down. I also used the magazine-wrap plastic as well as cling film.
The results were similar to before however the most effective, in my opinion, was when I used a diluted top coat as more of the previous layer shows through.

Diluted India ink over bright acrylics and magazine wrap plastic . . . I forgot to dilute it before application so I spritzed it with water.
Wendy @ Late Start Studio

Brights over black gesso and magazine-wrap plastic. Unfortuantely I put the black smudge on after with my grubby fingers.
Wendy @ Late Start Studio

Even the magazine wrap plastic looked interesting after I’d used both sides . . . I’ll probably use it again knowing that it will leave remnants of colour behind. Hmmm . . . I wonder if I can stick down with a matt gel?
Wendy @ Late Start Studio
I used Atelier Interactive acrylics for these samples. I bought them myself however if Atelier wants to subsidise my play experiments that would be lovely!
And now that my curiosity has been satisfied it’s time to put all my paints away otherwise I won’t get some presents made and of course I can’t tell you about those because my family read this blog. Maybe I’ll lay our some cardboard first and make gift tags . . . I’m thinking of white under and over pastels. So just a little more playtime perhaps or is this perseverance beginning to blossom?