Thursday, January 19, 2017

January 15th Hint of the Week

 When to use Magic Water? (From Lakeside Pottery in Stamford, CT)

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:
  1. 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).
  2. 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).
The above two conditions are more susceptible to cracking because when one piece is dryer that the other, it is therefore shrunk more than the other and will not continue to shrink uniformly after they are attached to each other, thus - creating stress.

Consequently magic water is great for mixing with your clay to make “magic” slip to attach all your handles, spouts, sprigs, etc. It really works better than just plain water in your slip mix. So Magic Slip could be your go to slip for all attachments.

Magic Mud? Magic mud is the same as your slip, magic water and clay, but it is thicker almost like toothpaste. Magic mud can be used for 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. You can fill in stress cracks during drying and additional stress cracks will be reduced 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.

We keep a couple of milk jugs of magic water made up and on the shelf in the ∆10 glaze area. Bring a small container and take what you need for mixing in your slip. It is cheap and easy to make and we try to keep the magic water jugs full.

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