This is what solder paste looks like in the wild. It’s a mixture of metal alloys: 96.5% tin (Sn), 3% silver (Ag), and 0.5% copper (Cu). Most paste has an expiration date and should be stored in a cool place. This has to do with the flux that is added to the metals thus creating the paste consistency. Flux changes the surface tension of the metal when it is in liquid form helping it to flow into the joints.