Scola air hardening air drying clay terracotta amp stone scola adc125kg scola air hardening clay has all the qualities of traditional clay except that it doesnt require firing making it ideal for younger and less experienced modellers it is reinforced with synthetic fibres for additional strength and a low shrinkage rate drying time will obviously vary according to the thickness and size of the model incomplete models can be kept workable under a damp cloth so that modelling can be