Evil Mad Scientist. The process was fun. I put some engineering and trade terms on the hearts for a good laugh. This year, in keeping with the conversation hearts Valentine tradition, I wanted to make a large sign (or several) that looked like the candy.
I've created temporary molds before, usually destroying the mold in the process. However, this was the first time I've tried to construct one out of craft foam and I hoped that the mold could be reused. The foam surface, I reasoned, would give a nice matte finish to the plaster and that was the ideal surface finish on which to use a gritty chalkboard paint. Modeling clay was used to temporarily "mortar" the pieces together and the mold seemed fairly solid. I just had to make sure I used plenty of clay and pressed it around the edges well to seal he gaps. As you can see, the mold worked!
Originally, I intended to simply paint my heart and stamp a phrase onto it. However, I wasn't sure what message to use. I wanted to be trendy but I also didn't want to have to repaint it every year to keep it modern. So I decided to use colored chalkboard paint which would allow me to add new phrases anytime I wanted. Thanks to Martha Stewart's instructions for custom colored chalkboard paint, I was able to create a durable finish with a small bottle of acrylic craft paint and some tile grout.
For full details, including pictures, please visit my Chalkboard Conversation Heart Instructable.