I bought a pack of six marbling inks and a few inking trays for under £10 (around 15$) as I wanted to experiment with this process in a hospital setting where I run creative activities with young people.
I hadn't done this since I was a child and loved the instant result!
Just add a cm or so of water, add droplets of ink, leave them to swish around, blow them or drag with a cocktail stick and you're ready to marble.
Lay some thick cartridge paper on the water surface and it literally lifts the inky pattern off the water.
I'd like to research into some techniques for next time.
Here are some of our first attempts, I'm going to do it with my kids at the weekend - can't wait!