I was just going to put up John's suggestion. A 3" long chunk of 1-1/2" PVC, you can cap or plug the bottom with your prefered meathod and mix away! The best results I get are from purposely over mixing a pen pour and dumping the left over in the PVC "mold". PR shrinks when it's dry so you can just smack it out on the bench or shoot some Pam in the mold...it won't react with the resin. Like John said...there are no limits...2 part pour, black on the bottom, let it cure. Get a bottle cap from your beverage of choice, set it on top of the black and then pour clear over the black and cap...Shazzam! Put in a bug, bee, fly, stone, Jell-o...whatever floats your boat. My brain just over loaded!