Thursday, August 28, 2014

June Hints of the Week

June 2nd 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:
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).

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.

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).

[*We make Magic Water for you at the Clay Arts Guild. It is in containers in the high fire glaze room. Just fill your own container with what you need. If it is gone let us know and we’ll make more.}

How to make Magic Mud - Recipe?
Chop up 1/4 to 1/3 of a cup of either paper napkin, toilet paper, or paper towel
Add 3/4 to 2/3 of a cup of bone dry clay hammered into small pieces, or powdered. It is better to use the same clay for both, magic mud and your actual project.
Soak overnight in Magic Water poured one inch above clay and paper mixture.
Blend in electric blender
Pour off excess water
The slip created is ready for use


June 10th Hint of the Week
Plaster can be “poison” to pottery. If even a small amount of plaster inadvertently gets into your clay it can be disastrous. Plaster absorbs too much water, causing drying cracks and will probably explode or pop off chunks of clay when fired. Plaster is useful and important in ceramics for molds, wedging tables, drying wet pieces and for ware boards, etc.
It is not a good idea to use metal tools on plaster molds, wedging tables and clay bats as there is the potential to chip or scrape plaster into your clay.
 

Work with plaster away from clay and clean up the area thoroughly. Put down a plastic tarp on tables if you are working with plaster, otherwise the plaster will get into the canvas on the table. The same goes for “Alumina.”
 

We encourage the use of drywall boards to help dry clay. If you do use sheetrock, “drywall” or gypsum boards, to dry clay or for ware boards, make sure that you seal all the exposed plaster edges with tape. Otherwise you will leave loose chunks of plaster around. Be on the look-out for bare edges tape them up with Duct Tape.
 

We have large pieces of sheetrock “drywall at the guild which have been donated for member to use. There was some in the electric kiln room and in the back of Bill Ramsey’s studio against the wall to the northwest of the furnace. These are for your use and you are welcome to cut off whatever you need.
Be sure to cut sheetrock in an area where plaster won’t get into clay or on surfaces where clay will be worked.
Clean up the plaster dust when you are done and tape the exposed edges.



June 18th Hint of the Week
How to Re-Glaze a Piece (BigCeramicStore.com)
First, note that this process is never predictable. In most cases you can make a new piece in less time than you can spend re-glazing it, with much more predictable results. But sometimes there is that piece you can't part with and really want to re-glaze. Here are some things you can try to increase your success rate. The goal, of course, is to get the new glaze to stick to the old glaze.

· Spray the piece with spray starch, let dry, and then re-glaze.

· Spray the piece with sticky hairspray (usually the cheapest you can find), dry, re-glaze.

· Heat the piece first, with a heat gun or in the oven or kiln.

· Brush white (Elmer's) glue on, let dry, re-glaze.

· Microwave the piece for 30 seconds. (Some potters say this makes a huge difference, and the piece doesn't need to actually get or stay hot)

· To improve your odds further, wash the pot first with ammonia or detergent, wearing rubber gloves, and don't touch it. The oils from your fingers can prevent glaze from sticking.

· And... Don't use too much of anything. If you get the coating too thick, you may prevent adhesion instead of encouraging it.


No comments:

Post a Comment