I bought a 36 inch diameter rubber balloon to test both its lifting power and its ability to hold helium under pressure. The problem with helium is that the molecules are so small they seep through most otherwise impermeable materials. I filled the balloon (by chance it was red) 4 days ago. I tied it to the most massive tablet I had. it lifted it! so I’m on the right track as far as volume of helium needed to lift the clay. The problem is that in the four days the balloon lost about half the helium. That rate of loss is too much for me to seriously consider using rubber balloons. The properly sealed mylar balloon I inflated about three weeks ago has only now lost about 1/4 of its helium. I have a number of 36 inch mylar balloons to pick up tomorrow.
Attached is a link to a video I shot today at the end of my test.