I used paper of my own making for this technique--it's actually recycled recycled paper. The paper is computer paper that had been in the scrap pile, then used for colorful techniques. Some of those color catchers turn out to be pretty and I squirrel away the pretty pieces knowing I will find a good place to use them some day. Today was one of those days. So all those colorful bits on this background are torn pieces of color catchers.
The Serendipity technique is not hard. It is time consuming. The hardest part is deciding what papers and images to put together. The rest is just tear and paste.