If you've never used shaving cream to marbleize your papers, then you must try it. It's amazing every time.
Shaving cream is one of those fun materials that kids love and the state says is not to be sprayed in front of kids. So, check with your state rules and find a way to use it. I had to spray it in the hallway or before the kids were in the classroom.
We sprayed shaving cream on a plate, you can use a tray, to contain the shaving cream. You have to let them play with it for a while. Then have them spread it out smooth and somewhat flat.
We used eye droppers to drop paint onto the shaving cream, liquid water colors work best. I didn't have any so I tried watered down washable paint and tried it with food coloring. Both worked okay.
Then, use the end of a paint brush to swirl the paint around.
Place paper on top of shaving cream pressing lightly. You can wipe the shaving cream off to get a wet marbled look.
Or, let it dry and rub off extra for a more exact copy.
We then cut out a fish shape.