Here's how this was done. (Polymer Clay & Alcohol Inks)
Polymer clay is genuinely the most versatile products to have ever entered the craft world and it happened decades ago.
Roll out black clay for backing. (Medium setting on PM)
Roll out white clay and place over the uncured black clay. (Medium setting on PM)
Roll over both to adhere. (Not flatten)
Squirt alcohol inks over the white clay and use an air-can to move the inks around.
Use a cut out of choice. (Here hearts and circles were used, but you can see that.)
Put a bail on the backs of each heart.
Attach rubber cording to bottom backs of hearts and top backs
Cure according to clay manufacturer's instructions.
Alcohol inks are lots of fun. Any questions, send an email.