Calcium Carbonate (chalk) is used to produce good colours when dyeing with madder & weld and provides hard water conditions (see Dyeing with Madder and Dyeing with Weld pages).
The Calcium Carbonate is weighed and packed in a polythene grip-seal bag. The bag is then labelled and put in a second grip seal bag for extra protection. I then place the packet in a small padded envelope and post it to you First Class.