There have been many interpretations of the technique called Serendipity.
This is my favorite method.
Start with a full 8.5" x 11"
sheet of black cardstock.
Use scraps, in a momochromatic theme.
Tear scraps very randomly, and cover back of each piece with glue stick- be generous with glue.
Place all over cardstock in a random design, overlap some, but allow the black cardstock to show through.
When sheet is covered, turn it over and burnish the back. (rub with a bone folder all over the back)