Taken from http://www.lakesidepottery.com/HTML%20Text/Tips/pottery-magic-mud-magic-water-paper-clay.htm
When to use Magic Water?
Magic water is used when the bond between two pieces of clay is a suspect for cracking during drying or bisque firing. Cracks can occur in the following conditions:
- When one piece of clay dries faster than the other which typically occurs when it has a smaller mass or thinner than the other piece (e.g., a mug handle).
- When one clay piece is applied to another piece that is already a dryer leather-hard (e.g., when waiting is required for a thrown pot to harden before applying hand-built piece).
When to use Magic Mud / Paper Clay?
Same as above with more extreme cases. It enables the joining process to be less critical and therefore one can build more spontaneously as well as build wet clay on dryer clay. Stress cracks during drying reduce dramatically. It can also be used to connect broken bone-dry pots / sculptures. Sometimes it works fixing broken bisqued pots (needs to be re-bisqued after applying magic mud). When fixing broken bone-dry or bisqued pot, always apply more magic mud / magic slip than needed and build the layers slowly allowing the layers to dry in between applications. The excess slip can be filed down after the bisque firing.
Why does Magic Water work?
Sodium in the soda ash and the sodium silicate is a very powerful flux. The silica in the sodium silicate adds some glass-former. The water is to dissolve the soda ash (which is soluble) and therefore travels a little way into the wet clay. The sodium silicate is sticky and dries really hard and faster than the clay does. The end result is that the Magic Water makes a sticky layer of almost-glaze that soaks into the surrounding clay and dries hard. Thus, cracks are prevented in the drying and the bond is stronger after firing.
Why does Magic Mud /Paper Clay work?
In addition to the reasons mention above (Magic Water), the paper fiber will bond the two pieces of clay better and resist stress more effectively during the clay drying / shrinking process (has no effect during firing).
How to make Magic Water - Recipe?
How to make Magic Mud - Recipe?|