Plus Self Hardening Clay is a natural modelling clay that has a high durability once it has fully hardened. No firing is necessary for this natural black clay- simply create your model, let it harden and you will have your own clay model with minimal effort! You can varnish this clay when finished for a superior finish, plus any leftover clay can easily be stored in an airtight plastic bag. Colour in your dried clay with paint or crayons to decorate after it has dried!