Art journalists are intimately familiar with the joy of a simple plastic card. Used gift cards, hotel room key cards, supermarket rewards cards. All good. We collect them like we collect paint chips at Home Depot. These are used for an wide number of techniques. You can use them to stamp lines for journaling, scrape texture, scrape lines, edge photos, edge pages, apply extensive layers of gesso, matte medium, acrylic paint, paint grids...
The prompt is to use the edge of an old credit card or plastic card to apply paint in any way you wish.
Todays rules: No brushes, no fingers, no other tools to apply paint. Try to get as many effects as you possibly can. Think angles, lines, curves, criss-crosses, multiple colors, etc. These tiny envelopes are called "coin" envelopes, aren't they cute? You could attach a tiny envelope to your art journal page (with a secret inside, maybe), decorate a large envelope to mail the next birthday card you send out, or simply put lines and marks on an art journal background.
Spread a line of fluid acrylics straight from the container.
Dip the edge of a plastic card in the paint and "stamp" to make a line. Slide back and forth if needed.
To create a larger area of paint, dip in the exact same way, but pull the edge of the card down and across the paper to paint.
All created with a plastic card and Golden fluid acrylics.
If you love using plastic cards instead of brushes for your art journal pages, here's another fun technique to create lines and borders on your pages from my 2011 21 Secrets Workshop Urban Layer Cake, focusing on techniques for adding layers, texture and visual interest with acrylics with a plastic card. The instructions and videos are now available free!