Monday, May 22, 2017

Hint of the Week

How to Dry a Platter Without Cracks

 by Mea Rhee, Good Elephant Pottery, 05/30/2010

Here's what works and what doesn't, after months of trial and error. I'm talking about wheel-thrown serving platters, between 16 and 20 inches across when freshly thrown. Until this year, I rarely threw platters this large. They cracked while drying on a regular basis, I'd say 1 out of every 4 developed a crack in the middle of the floor. I considered the cracks to be random occurrences, because I had not bothered to analyze the problem. This year, as part of my wholesale orders, I needed to produce roughly a dozen big platters. When two of the early ones cracked, I started looking for answers. And here's what I figured out.
First and foremost, a large platter requires good throwing and trimming. It must be evenly thick throughout, and well-compressed as it is thrown. A thin area will crack, and a thick area will crack, because these cause uneven drying and shrinking, which the clay cannot tolerate. This factor requires experience and good technique, which every potter possesses in different amounts. But here are four factors that everyone can control right now:

1. Dry the platter on a melamine board. Melamine has a non-absorbent hard plastic surface, with a slightly grainy texture, that does not bond with leather-hard clay, therefore the platter is free to shrink as it dries. The other choices in my studio are wood and drywall, which are useful for other pots but not for large platters. A wood board warps when it becomes damp. A drywall board doesn't warp, [but its paper surface becomes spongy when wet and the platter may stick].

2. Dry the platter on its rim. All pots dry from top to bottom, and a rim dries much faster than a floor because its surfaces are more exposed. So drying a platter upside-down evens out the drying process. When dried right-side-up, the rim will harden and shrink much faster than the floor. When the floor tries to shrink later, the hardened rim does not allow it, and the floor splits open.

3. When the platter is upside-down, support the floor. Before I flip a platter over for trimming, I stack a combination of studio sponges, upholstery foam, and 1/4 inch thick scrubber pads, in the middle of the platter flush with the height of the rim. So when the platter is upside-down, the floor is supported from underneath. Without the support, sometimes the floor of the platter would sink downward while trimming, and these platters were guaranteed to crack later. My (unsubstantiated) explanation is that the flexing caused micro-cracks in the leather-hard clay, which grew into visible cracks later. I leave the supports under the platter for its first few days of drying. As soon as the platter is stiff enough to be picked up, I remove the supports so there is nothing to prevent the platter from shrinking.

4. Cover the drying platter with fabric. My basement studio is very drafty, and uneven drying is a constant battle. But a sheet of fabric is all it takes to slow down and even out the drying process for a platter. Any lightweight fabric works, like an old t-shirt or bedsheet. A sheet of plastic also works, but it slows down the process too much. Using fabric, the platter is ready to fire in 8-9 days. Using plastic, the platter takes 3-4 weeks to dry, unacceptable for a wholesale schedule.

All of these techniques can be summed up thusly: even out the drying process, allow the pot to shrink, and don't allow the pot to flex. I am happy to report that after incorporating all four of these factors in my platter-making process, I have not lost a single platter!

Tuesday, April 11, 2017

Hint of the Week

Acrylic Paint on Pottery by Susan Hickman

Glazing can be frustrating since the color you paint is different than the final product. However, you can paint non-food items that will be indoors with acrylic paint. For containers, you may want to glaze and fire the inside before you paint the outside. These sculptures were painted with ceramic craft paints after their second cone appropriate firing. If you want a glossy finish, spray with Krylon clear gloss 2X. You can forego the clear spray paint, use a matte or satin clear spray, or coat with an acrylic glaze.

Check with Susan Hickman if you want more information. This is not “against the rules”. You will find many examples of painted sculpture in ceramic magazines.

Here is another piece that has been painted with acrylics. It is a “lantern” with a light inside. It is one of those battery operated push button globe lamps in the bottom. The inside of the lantern is painted white or could be glazed white, but the outside is painted with acrylics.
First lantern picture to the right is with the light out and the second shows it with the light on. 

CAG Swag

SHOWING OFF THE GUILD Advertise the guild by wearing a shirt or hat. Susan Hickman has four designs for you to choose from. You will find several styles of clothing and a wide variety of sizes and colors with Clay Arts Guild on them. We would like to see our members showing off the guild around town and at pottery events. The Clay Arts Guild designs are offered at base price. Susan does not receive any money for guild designs. You can order your guild items here:

Tuesday, February 7, 2017

Got Primitive

Day class on Anasazi pottery yesterday by Gene Hickman!! It was fun to see our finished replicas too!!  Gene has some nifty stuff on pinterest also.

Monday, February 6, 2017

February 5th Hint of the Week

Tips On Plates & Platters

 - Pottery Magic

Making plates can be tricky, and the larger the plate the more likely you will encounter problems. Here are some remedies:
  • Make sure the clay is thick enough. Thinner plates are more likely to warp. Thickness should be even. Clay should be very uniform, work the clay well.
  • When rolling slabs, make sure you roll it out evenly in all directions, otherwise you could compress one side more than another and or have thinner places on one end or another.
    * When throwing, use soft clay but not too much water or the rim will get too floppy.
    * When you carry your wet clay slabs to a different place to form, make sure you don’t stretch it. Put it on a board, or roll it lightly into a sausage, then unroll directly on the mold that you will use.
  • Plates must be dried very slowly and evenly. Uneven drying can set up stresses that don't show themselves until the final glaze firing.
    * It can help to control drying so the center dries faster than the rim. To do this, cut a round hole in the plastic about 3-4 inches in diameter over the center of the plate.
    * Some people use water based wax to coat the rims during drying, to prevent them from drying too quickly.
  • For large platters, you probably need two foot rings, one around the outside and a smaller one left in the center. Otherwise the center of the plate may sag during firing.
    * When you place a platter on it’s rim, place it on soft foam to protect the rim and keep it from getting stressed.
    * Trimming large platters can cause slumping of the bottom during the trimming process. You can put layers of foam rubber or carpet pad into the center area before inverting * *  * * *Place a board onto foam rubber or rim then invert the whole thing to turn it over. This “holds up” the center area and prevents it from sagging. It is not necessary to fill the whole center of the plate. If you fill the center only (i.e. a 6” circular piece of foam rubber), it will keep it from sagging.
    * Another thing to use in a similar way is socks or larger fabric sacks filled with rice. The rice is malleable so you can push it around until you get the right shape.
    * Or still another item to use is a sponge.
    * Sharp tools make it much easier to trim without causing deformation. (Remember, clay has memory and even if you smooth out any deformations, they will come back during firing.)
  • Many people find firing goes much better when they notch the plates' foot rings. Warping, cracking, s-cracks, were all eliminated. The notches provided a way for air trapped under the foot to escape. If the gas can’t escape from bottom it may cause the center of the plate or platter to “bow” up. Just make small, U-shaped notches at the bottom of your foot ring.
    * Instead of, or in addition to these notches, drill small holes in the foot ring. This also allows the gasses and heat to escape, and also allows for a wire to be used for hanging. This is especially nice for plates that are too large to fit into standard upper kitchen cabinets. Some people use a single hole, others two close together, others 3 spaced evenly around the platter
  • For plates and other items with large bases, make a clay “cookie” at the same time as your piece. This is a sheet of clay (the same type of clay), which you sit your piece during drying and firing. The cookie and the plate will shrink at the same rate. This seems to keep the piece from “hanging up” on the kiln shelf during shrinkage, expansion and contraction. For extra assurance, put a wash of alumna hydrate on the feet and the cookie.
  • Another method is to cover the shelves with grog. The folks who fire the kilns will put the grog on the shelf under the plate, just leave them a note.

January 28th Hint of the Week

How to: Make a texture roller for clay

This project is instant gratification. Something that is not that common in the world of clay. With this texture roller, you can use it as soon as the hot glue has cooled, which is very fast. It’s a great project to do in a class, or on your own so you have a custom tool that no one else has.

§  a roller of some sort (cut up pieces of PVC, empty rolls of tape, couplings for PVC, plastic      rolling pins from the dollar store or craft store).
§  a sharpie.
§  a hot glue gun. They only cost a couple of bucks.
§  extra hot glue sticks.

Draw your pattern onto the rolling pin. It’s easier to work out the pattern before with a Sharpie than it is later with the hot glue. Think about some sort of connected pattern, they tend to have the best results. And don’t go overboard with the lines, you’ll regret it later. And remember that the hot glue line aren’t going to be perfect, so just go with the imperfection.

While you’re drawing, plug in your hot glue gun. Make sure that you do it on a surface that you can toss when done, like newspaper or cardboard. When you’re done drawing on your design, start gluing. Be a bit heavy handed with the glue. If the lines are too thin, they won’t show up on the clay as well.

After the glue seems cool, start rolling away… The first attempt might stick a bit, but after there is some dusty clay on the roller, it won’t really stick.

If you’re not a hand builder, a nice use for one of these textured slabs is in the bottom of a thrown and altered casserole.

For the throwers out there: If you use a small print roller with a handle to put the design on, you can hold this against the side of a freshly thrown pot while supporting the pot wall from the inside.