Pure potassium is much more fun when water is applied. Take one pound pure potassium, insert into a flask in pea sized chunks, insert a stopper with two holes, insert a glass tube into one to inject water onto the pellets, insert a glass tube in the other to carry away the hydrogen.
Use a flame hood when applying a bic lighter to the device.
Our teacher kept the sodium and potassium locked up.
One of his favorite tricks to impress the class was for us to all go outside where he would set down a pan of water and then throw in a pea sized piece of sodium. A split second later there was a explosion as the exothermic reaction of the sodium producing hydrogen ignited said hydrogen. I seriously doubt that he’d be allowed to do that today.
I remember the sodium was so reactive that it was stored in a metal can and submerged in kerosene. I figured that since calcium is far less reactive it might be a better choice.