This is an example of an alcohol ink background. If you haven't tried this technique yet, you are in for a treat! (I will be blogging a basic "how-to" in the next several days) And trust me, they are IMPOSSIBLE to duplicate! This is also what makes them so beautiful - they are absolutely one-of-a-kind-UNIQUE! Because of this, it was suggested to me, if you want several cards to have a similar "look" - line them up in multiples and layer your colors as if you were working on a single card.
Most of my ATCs are made using playing cards. I find that it not only saves time cutting, but they provide a sturdy base with a nice substantial weight or feel to them.
I've purchased white cardstock "ATC blanks" in sets of 50 - 100 and have been QUITE disappointed with how flimsy they are. I feel the same about patterned scrapbook paper, that it lacks sturdiness. But LOTS of artists use pp with stunning results.
Suggestion: buy small quantities of blank ATCs online or in stores, of 10 - 25, and create with them before buying large quantities. (cost is approx $4 per 100) The same goes for matt or illustration board, which could prove to be too heavy or too thick for your liking.
Some artists are quite happy cutting up cereal boxes. I've even tried PIZZA BOXES! All part of the journey!