The Magic of Soluble Metal Salts

摘要

I have been a studio potter in Berkeley, California for over thirty years and solubles have long been an interest of mine. They are not really magic, but they are capable of very unusual effects. Understanding them is really a matter of making tests to find out what they can do, much like anything else in ceramics. For those not familiar with the term, metal salts are the nitrate, chloride or sulphate forms of the metals more commonly used in ceramics in the carbonate or oxide form. Besides being soluble in water, the salt forms act quite differently from oxides and carbonates in many ways. Some can form haloes of colour (image 1) when applied over other colours, and mixtures of solubles sometimes form two, and even three colour haloes. Some produce a colour with soft diffuse edges (image 2), while others leave a crisp edge. Phosphoric acid will displace the colour it is brushed over (image 4), leaving a colourless centre and a dark edge at the boundary of the brush mark.