Soluble Salt has been used in ceramic decorating for a long time, but it’s relatively new to me. Ferric chloride and copper sulphate are good examples of soluble salt I use often in regular pit firing. 
However, the way soluble salt was used on these vases, is not like the “sprinkle it on and let it be” style. They were actually carefully applied on to the pots with brushes, and fired in a control raku kiln. There are degree of control here. 
These vases were fired in a group workshop and many potters including myself worked together to experiment this technique. And we learned just how many possible outcomes there are, by just applying thinner or thicker; or firing just 100 degree Celsius differences. 
Nevertheless the outcomes are very interesting, and I would very much like to give it a try combining with pit firing in the further. 
Due to the low firing method used on these pot, they are for decoration only, and do not hold water.