DIY Fluffy Slime Kit - 24 Colors Slime Kits for Girls Boys Toys with 48 Glitter Powder,Clear Slime Supplies for Kids Art Craft,Includes Air Dry Clay, Fruit Slices and Tools,Squeeze Stress Relief Toy, Clay,Crystal

Q: Do the color containers have a reusable lid? Could this be used as a class pack with each student getting one color?

Yes all the containers have reusable lids.

Q: Does this kit expire?

The box does not list an expiration date. However from my own personal experience the longer the slimes sat unopened or not the more jelly like and solid they became.

Q: does the slime eventually harden so that the projects remain solid once they are made?

Dear Customer, Due to the texture of the slime itself, your designs will not remain solid soon after completion.If you want to achieve a more stable effect, it is recommended that you mix the slime with the super light clay we provide, so that the projects will be more stable.