The dreamy curves of marbleizing lend themselves to a number of decorative paper crafts, such as this Valentine's Day card with a heart cut-out. 

First, learn how to make marbleized cards. 

After you marbleize the paper and let it dry, cut a piece of white card stock 3 1/2-by-8 inches. Fold in half, scoring with a bone folder. 

Cut a piece of your marbleized paper to 3 1/2-by-4 inches and trace a heart shape on the back side. Use a craft knife to cut out the window. (To make a heart-shaped template, fold a piece of paper in half and cut out a simple heart.) 

Next, with a glue stick, glue cut-out paper to the cover of the card. If desired, stamp the words "Be Mine" using alphabet rubber stamps.