STEM Students made cartesian divers out of glass tubing. This required some sealing and blowing the glass into little bulbs. A new and tricky skill! The Cartesian diver experiment demonstrates gas compressibility and buoyancy using a small, weighted object (the "diver") in a sealed bottle of water; squeezing the bottle increases pressure, forcing water into the diver, making the trapped air bubble smaller, increasing the diver's density, and causing it to sink, while releasing pressure allows the air to expand, decreasing density and making it float, similar to how submarines work. We had a few failures but successfully made three working models.