Design from the Least Expected Things

This is my recently completed piece. It's bone dry greenware and ready for bisque fire.

The base piece (the honey comb looking thing) started out as an experiment using cardboard packaging and coating it with paper clay slip. I have not done this before and wanted to try it out to see what will happen and how it will hold up in high fire to Cone 10 reduction.

I like the shape of it and where it was going so I decided to make it more complete by adding some of my trademark organic pods.

This piece will be essentially white on white with no colored glazes. The pods have been dipped in a beaded white glaze. At Cone 10, this glaze will "bead up" and crackle, so I hope. By using paper clay, it is possible to do a one-fire from greenware directly to Cone 10 and bypassing the bisque fire. However, since I fire most of my works in a community kiln, they may not allow me to do that.

I'll post the finished piece when I have it all completed.

Structural Support Considerations

Whenever I build my pod shaped vessels, I have to think about how to fire them in the kiln for bisque fire and at higher cones, for example at cone 5 or cone 10.

In this piece, I wanted to use the Van Gilden’s flashing slip which cracks really nicely at Cone 10 so I had to design a structural support system that will be strong enough to survive a Cone 10 fire.

The donut ring and supporting tubes were all assembled from bone dry paper clay pieces using dry to dry techniques (top picture).  

As my pod is rather heavy and tall (36” high), my support has to be well constructed to withstand any movement in the kiln during firing. The legs were thick slabs rolled into tubes.

Lateral struts at the bottom were added to give sideways rigidity.

This is structural support for my pod which can be seen in the background. The Van Gilden's flashing slip has been applied to it. It's bone dry and it's ready for bisque firing.

 In a way, the structural support is like a piece of sculpture in itself. I plan to reuse this support for future works.

From Flat Mesh to 3D - Part 3

This is my new teapot project after completing all the dippings in paper clay slip. The teapot and the base are separate pieces. I decide to build the base for the teapot to sit on and to elevate it off the ground.

It took me 19 dips over a span of 8 days in the Gault 1o paper clay slip and about the same number of dips over 4 days in the Southern Ice Porcelain paper clay slip (thin consistency) to achieve this.

I used the Southern Ice porcelain paper clay slip for the final coats because I really like the brilliant whiteness of the porcelain paper clay when it is bisqued fired to Cone 04. One of the properties of paper clay is that you can add wet paper clay (in the case, slip) to a bone dry piece with no problems at all. The piece is bone dry and ready for bisque fire.

It's a sculptural piece, a take from my earlier work titled "Empty Calories"

Paperclay & Shrinkage

One of the things I get asked with paperclay is "How much does it shrink?" That is a valid question and after all, it's good to know all the technical details of the clay when one is working with it.

The paperclay and subsequent technical infomation provided here is manufactured by IMCO in Sacramento. It's a proprietary blend and is carried locally here in So. Calif by Aardvark Clay Company in Santa Ana, in 25lbs bag.

The information provided here is from my own experience.

From green to bone dry - 5 %

After bisque - not measured

After high fire (Cone 10 reduction) - 10%

Total shrinkage is around 15%

Considering other traditional clay bodies (total shrinkage ) is anywhere from 8% (low end) to 12-13%(high end), this paperclay shrinkage is quite a bit. It's good to know so you can compensate by making your pieces a bit larger than you normally would.

Blow Out Big Time - sometimes even cooked rice does not work!

This is one time when even cooked rice added to my paperclay did not survive the bisque fire. Large chucks from the sides of my hand pinched bowl blew out during the bisque fire. I cannot figure out what is causing this as the piece was bone dry when it entered the kiln. It had also been drying in my studio for several weeks prior to the bisque fire. These kind of failures happen once in a while (about 5 - 10% of the time) and I'm still trying to find out the common underlying factor.

I use left over cooked rice and sometimes I let the rice dry out for several days. When I leave the rice out for too long, they start to dry out and get hard and crusty. Then I rehydrate them to soften them up again so I can wedge them with my paperclay. Could this affect the outcome? Perhaps some moisture still remains within the clumps of rice causing the blow out.

This method of making my hand-formed bowls and cups takes so much longer to make than if it had been thrown on a wheel. The successful end product, however, it worth the effort.

Perlite and Paperclay - Part I

I've used several type of inclusions with my paperclay. They range from sawdust, wood chips, straw, rice hulls, and cooked rice. Recently I had a chance to try perlite mixed with my paperclay. Perlite is an inorganic material that is used as a conditioner to improve the aeration and water retention properties of soil. I got my bag of Perlite from Home Depot in the garden department. In this test, I was curious to see what the voids look like after the bisque fire.

The picture on the left shows a simple pinch form made from paperclay mixed with perlite. The amount of perlite used is just an estimate; enough to give some kind of texture. It survives the bisque fire without any problems. The form is extremely light. After sanding the outside surface of the form with a metal rasp, the random voids can be seen.

Compare this with the sphere on the right side (it's part of a sculpture I'm currently working on). It this piece, I used paperclay mixed with cooked rice. The mixture was applied as a thin coat (about 3/8" thick) over a bone dry paperclay sphere using paperclay slip as "glue." Many more regular shaped voids can been seen all over the bisqued surface of the sphere after sanding.

I was hoping to see more irregular voids from the perlite. I do see that some of the perlite still remains trapped in the bisque ware. I find the perlite from the bag is more varied in size, some ranging from size of coarse sands to around 1/4" in diameter.

I want to take both of these to high fire (cone 10 reduction) and am curious to see how the perlite behaves. I know how the paperclay mixed with cooked rice will behave as I have been using this technique for several years. I'll post another entry in the blog once I have completed this test.

Applying Fresh Paperclay onto Bisqued Surfaces.

I decided I wanted this pagoda design on the current sculpture set I'm working on, but the pieces have already been bisqued. The base clay is Bmix and sand, and I've applied a white slip over it in the green stage.

Tracing of pagoda design onto bisqued piece with graphite paper.

Originally, I was thinking of doing a wax resist or a stencil treatment with the design. I opted for the dimensional effect I was able to achieve with my "Take Out Tea" sculpture.

The paperclay slip I use is the Southern Ice Porcelain paperclay. The slip is consistency of heavy cream and blended well to remove lumps. I use a squeeze bottle with a small nozzle - the ones you use to do slip trailing. The design is first transfered on to the bisqued piece and the slip trailing is done free hand. Successive coats are built up to achieve the desired raised effect. Since slip is mostly water, it takes several coats to accomplish this.

What I found is that if my slip is too thick, the edges then to curl and peel from the bisqued surface. Wetting it down with a fine mist from a spray bottle helps. What works better is thinning out the paperclay slip till it's about skim milk consistency and then brushing over the design with a small brush. This thin slip still contains the paper fibers in suspension and this helps to "hold" your relief design in place. Both bisqued piece and the fresh dry slip being very "thirsty" sucks the moisture out of this this watery slip extremely fast. So far, my design has not exhibited curling or peeling at the edges.

After several applications of fresh slip. You can still see the tracing of the pagoda under the slip.

The next stage is to test this application by re-firing the piece at bisque temp and see if this holds.

After the bisque firing,  my added on design held and bonded with the base layer, showing no signs of cracking or lifting off. This is very encouraging! 

After the bisque firing, the graphite tracing burns off. The freshly applied paperclay slip is bonded onto the piece.

Paperclay and Cracking

© 2009 Anthony Foo.

The bane of all ceramic artists - CRACKING! There are many reasons why and when a piece cracks.

1. Crack during the drying stage - greenware

2. Crack after the bisque stage

3. Crack after the high fire (in this case, Cone 10) stage

What to do and how to mitigate the problem. The discussion here pertains only to paperclay, and is based on my personal experiences with the sculpture paperclay from Aardvark Clay Company, Santa Ana. IMCO (from Sacramento) is the manufacturer. I've been using this paperclay since 2004.

1. Crack during drying stage - from leather hard to bone dry greenware.

This is usually due to improper/weak joining, especially when you are doing dry to dry joints. Another reason is unbalanced/uneven drying once the joints are formed. There are 2 kinds of cracks here.

One is a surface crack formed primarily from not using enough moisture in your paperclay slips/slurry. The solution here is to use a thinner paperclay slip (ie more watery slip)  and cover/re-coat the cracks. It may take several applications to completely cover the cracks.

The other more serious one is the deep structural crack due to improper technique. I find that the only way to find out if this is a structural crack is to take a knife or similar tool and dig out the crack and see how deep it goes into your piece. If it is not too deep, the good news is that it can be fixed with paperclay. Remove enough of the dry paperclay until you do not see the crack. Make the hole/opening large enough to do a decent repair/patch job. If during this digging out of the crack, your piece/seam falls apart, then you really know you've not done a good joint. Don't worry. Don't panic. Just start over and this time make sure you spend the time making a good, strong joint with good technique. That's one of the advantage of paperclay. You just can't go wrong with it, and even if you did, it's fixable. This advantage alone gives me peace of mind.

Do not be stingy in your "excavation." Spritz the area well or soak the area with a wet paper towel and let stand for some time for the surrounding dry paperclay to soak up this moisture to create a better moisture balance. Use very "mushy" paperclay to fill in the hole you made. Keep the area moist as the surrounding dry paperclay will want to "suck" the moisture from this spot, so keep the water sprayer handy.

2. Crack after the bisque stage.

Sometimes, even with our best care and technique, we still get cracks in our pieces. Sometimes everything looks good in the green stage, but after the bisque fire, you notice the cracks. If it is a hairline crack, it's really tough to do anything about it. If the crack is large/wide enough to patch with paperclay slip, you may try that. I ususally use a very runny paperclay slip as filler. The bisque piece will absorb the water from the paperclay slip very quickly. Several coats may be necessary to fill the crack. It also depends on how bad/serious the crack is. To be sure my patch holds, I usually re-bisque the piece to test my mending. If it survives, it stands a good chance in the high fire; if not, it's better to remake your piece.

3. Crack after high fire.

This happens sometimes as high fire (Cone 10) puts a lot of strain/stress on a piece, especially tall, vertical pieces.  As sculptural pieces, there is no reason to take it to Cone 10. A Cone 6 firing will do fine. When you find a crack in your piece after a high fire, it's pretty much "putty/epoxy time." Unless your piece is meant to hold water (for example, an ikebana vase or something similar) I usually don't do much about it. Sometimes the crack adds character to the piece, sometimes it does not. At this point, you can't do much fixing it.

A very appropriate quote from my instructor, Julia Klemek, "Don't fall in love with your piece until it comes out of the kiln (this is Cone 10 fire)."