Sunday, September 17, 2017

Small Sculpture and Cracking Glaze

this sculpture with two others in 2015

I've been working on a couple pieces of sculpture since 2015. I built them in 2015, applied underglaze in 2016, but couldn't finish them until this year, maybe, because their surfaces are causing me an unusual amount of trouble.

the first layer of underglaze in 2016

The one that has caused me the most trouble is a simple vertical sculpture with three bulb shaped attachments. There's no problem with the structure itself, but I could not get underglaze to stay put. When I first applied underglaze, it seemed fine. I fired it in place, but when I went to apply a second coat of a contrasting color, the first coat started to crack off.

two layers of slip cracking off

I can't remember fired underglaze cracking off any other work I've done besides this sculpture and another made at the same time. Generally, if glaze or underglaze won't stick to a surface it is because there is wax, grease, or dust on the surface, but none of those substances should survive firing and scrubbing. I picked off the underglaze that was cracking and scrubbed the whole pot before reapplying another layer of underglaze, but after a second firing, that too cracked off in multiple places. 

slip cracking off

At some point in 2016, I got mad and just covered the whole thing with throwing slip. I didn't expect this to solve the problem, but I was annoyed and didn't want to look at the piece anymore. The throwing slip cracked too, of course.

wet slip (you can see the circles of underglaze through the slip) and dry, cracking slip from 2016

This year, I decided to wash off the slip and see if there was anything to be done for the piece. Bits of hard, fired underglaze were still cracking off and where they cracked, they left a sharp edge and change in thickness that would show up through a new coat of underglaze. 

grinding off the underglaze

I decided to use a wire wheel to grind off as much underglaze as I could. Grinding off the underglaze was satisfying but messy. Mostly the underglaze cracked off, sometimes it required grinding, and in one section, the red underglaze was adhered so well that grinding didn't budge it--at least the amount of grinding time I was willing to commit didn't budge it.

the red that wouldn't grind off

At the tight corners, the wire brush was too thick to reach the underglaze. As it wasn't cracking, I decided to leave it alone. The transition between the raised level of the underglaze and the raw ceramic was more gentle than where the underglaze cracked off, so I guessed the depth change wouldn't show through the next layer of underglaze.

the wire brushed sculpture

I kind of like the ground texture of the raw ceramic. The sand and grog has become visible as the smooth ceramics surface was ground away. The rougher texture makes the surface look like cement, but the overall result doesn't feel like something I had much control over. The hard-to-reach crevices show up purple and blue and the hard, irregular red section looks out of place.

the wire brushed surface

I decided to reapply a red underglaze over the body and purple over the already purple bulb/leaf shapes and just fire it with a gloss over the top of everything. The piece is now "finished." It doesnt' appear to be cracking, but neither is it all that exciting to look at. Though a lot simpler than many of my other pieces, its surface required much more effort than what shows up in the piece now.

the "finished" piece from 2015

As I was getting pictures ready for this post, I pulled the masking tape off of the other vertical sculpture from 2015 (seen in back right of the first picture in this post). I had masking tape in place to hold on a bike part I had epoxied in place to complete the piece. When I pulled off the masking tape, it pulled a cracked section of glaze and underglaze off the surface of the sculpture. Sigh.

glaze cracks show up (today!) in the other sculpture from 2015

Sunday, September 10, 2017

Ball Opener

picking out PVC pipe fittings

I made and started using this new tool, called a "ball opener" last month. I didn't know anything about the tool until I watched this Tom Whitaker video on YouTube:

The tool looked easy to make and I thought it might help some of my students, so I gave it a shot. 

my CPVC ball opener

In the video, Whitaker talks about using CPVC. I had some initial trouble finding the parts so I picked up PVC pipe and fittings. Then I found the CPVC and decided to make a version from both materials. The PVC is a little thicker and I was able to find a cross shaped center piece with four openings. The CPVC is thinner (though they are both labeled as the same size) and I only found a t-shaped center.

my double-ended PVC ball opener

Putting together the tool was really simple. I used a mitre box to cut the pipe and my husband had some primer and cement to attach the pieces. I made a mess with the primer, but the whole process was fast and easy.

adding water to the hole I started with the ball opener

The ball opener is designed to be inserted into a centered ball of clay on the wheel. The tool is pressed straight down in the center of the clay. Because the center pipe is slightly shorter than the side pipes, it will not hit the wheel head, but will leave a 1/4" or 1/2" floor in the clay. Then the tool can be pulled towards the body, opening up the ball of clay and leaving a flat floor.

opening out the floor with the ball opener

In the video, Whitaker suggests that using the tool is simple, which is true, and that the tool doesn't bounce around at all. I found that the tool did bounce, but I suspect some practice on my part will help with that. In my initial test of the tool, I only used it for roughly 15 pieces.

pulling the walls up with the ball opener in the reclaim bucket

Initially, I thought this might be an acceptable tool for beginning students. I figured it wasn't really necessary for me because I know how to throw. What surprised me is that it immediately improved my results. Out of 15 pieces I threw with this tool, 15 dried and fired through the bisque with no cracks in the floor. Without the tool I don't lose much, but I probably lose 10% to small s-cracks in the floor. 

oops, my recycled clay had some junk in it

I used both tools and both ends, which means that some of my floors were closer to 1/2" with a 1/4" wall, but still, no cracks. I even threw with some reclaim clay with no cracking. Additionally, throwing with this tool was faster. Usually it takes me longer to drill the hole, open the floor, and compress the floor. These steps were rolled into one fast step with the ball opener. 

feet with not cracks

The results were pleasing. I think I may make a dozen or so more of these tools to take to school. They won't work for bowls with rounded bottoms, but they might be a relief for students making cylinders. Students should probably still learn the old-fashioned way, but this is such a simple tool they could make one themselves for use after YVC.

Saturday, September 2, 2017

Finishing Sculpture from Last Summer


Last summer, I started building two large sculptures but ran out of summer work time before I could finish them. I was able to build the sculptures last summer and bisque them, once I got a new kiln. They waited patiently in my studio until June of this year when I was able to begin applying color.

the sculpture in progress in 2016

Planning Attachments

Last summer, while I was building, I planned to attach bike parts to both sculptures. I had been thinking about moving parts for some time and I knew I wanted to try incorporating small scale moving parts positioned like leaves on the stem of the taller plant form.

placing bike parts in their planned location

The bike parts themselves incorporate bearings and have a nice smooth spinning motion. Last year, I had thrown some round shapes on the wheel with the intention of using them on top of bike pieces roughly this size. I epoxied these round forms onto bike parts. Inside these forms I attached found objects and fired ceramic pieces to add visual interest and to hold up the "stamen" of the "flower."

spinning bike parts with ceramic toppers

Underglazing and Glazing

The underglazing process for this sculpture, like all my underglazing processes, took a ridiculously long time because I layer at least two colors on each part of the sculpture.

first layer of underglaze in the kiln

For this sculpture, I first applied green underglaze to the "stem" or "trunk" of the plant, yellow to the gear sprigs, and purple to the closed and open forms on top of the sculpture. I bisque fired these first underglaze colors in place, then applied off-white into the texture of the stem and red on the gear sprigs, interiors, and indents of the top forms. There are a few more colors applied and layered on the sprigs that are almost hidden inside the circle formed by the top forms.

first and second layers of underglaze in progress

Applying the red on the top forms was most difficult where the forms butted up against one another. It took me several days and I had to wipe off glaze and reapply several times. Finally, once everything was fired to my satisfaction, I applied gloss glaze on the top forms and the sprigs.

underglaze and glaze finished


Last summer, during the drying process, a small but noticeable crack developed between the two top sections. The crack was probably due to the heavy weight of the two top sections pulling down on either branch of the stem. I noticed it before the form was completely dry and tried to save it by adding clay and using fabric to put the two sides in traction. 

bracing the sculpture to try to prevent cracking

The repair didn't wholly fix the problem and I was left with a small crack between the two branches. After the last glaze firing, I mixed up some epoxy paste and pressed it into the crack. Once the epoxy set, I mixed some acrylic paint and painted the epoxy to match the underglaze.

epoxy on the crack 

The seam isn't noticeable at first glance, but I plan to further hide the repair by painting a matching off-white paint into the impressed texture to match the design elsewhere on the sculpture.

painted crack


After all the glazing and repair was complete, I finished attaching the blue flower shapes (a.k.a. "end caps") to their non-ceramic elements and then attached those to the sculpture itself. 

toppers (a.k.a. end caps) before being attached

I had built round shapes sticking out of the sculpture to which these bike pieces would be attached.

the round part onto which the bike part attaches

One major challenge was applying the epoxy so that it stuck to the interior of the bike part but did not stick to the outside that was supposed to move.
epoxy applied

While the epoxy set, the attachments had to be held in place with masking tape. Only three of the six attachments are set as of this writing, but all three of those spin freely. The others are setting with tape in place.

toppers being held in place while epoxy sets
My goal for September is to take some quality images of this finished sculpture and possibly finish the other large piece as well.

a funny angle on the almost-finished work

Thursday, August 24, 2017

Under Glazing Three-Color Pods: Part 2

pods with their final layers of underglaze, before final glaze firing
Over the course of several weeks, I applied the bottom layers of underglaze for a set of six pod shapes. I fired three of the pods to cone 06 and three to cone 04, which is a bit hotter. 

pod fired to cone 06 (left) and 04 (right)

The turquoise and red underglazes are darker in the cone 04 firing, because of the firing temperature. 

yellow underglaze being applied to turquoise

Now that the first colors have been fired, they no longer wash away when wiped with a sponge. At this point I was able to add the contrasting colors over the top of the red, turquoise and purple.

yellow underglaze applied, drying

I began by painting bright yellow onto the turquoise textured background. I tried to avoid getting the yellow on the red, with varying levels of success based on how long I had been sitting in the studio and how bored I was of the process.

close up of yellow underglaze highlighting turquoise texture

Once the yellow was dry, I gently wiped away it away with a wet sponge. The yellow remained in many of the holes, but was washed away from the raised areas, revealing the turquoise color underneath. In this case, the yellow wiped away somewhat irregularly, both because the texture is irregular and because it is difficult to use even pressure with the sponge in the cramped areas between sprigs.

wiping yellow underglaze

The results vary now because of the temperature to which the six pods were fired, as well as because the slightly different shapes and spacings left the yellow more visible in some areas and on some pods than on others.
yellow layer complete

Next I applied dark blue onto the red sprigs, carefully avoiding the yellow and turquoise background. 

blue underglaze applied

The process took a long time and to save my aching back and to make myself feel better, I moved to the couch for some of the blue application. There the cat kept me company.

applying blue underglaze with my helper

At one point, a friend stopped by. I kept applying blue while I talked with her. As she was about to leave, I took the now-blue pod into the other room and brought back a pod with red sprigs as yet uncovered. At first, she thought it was the same pod and the color had changed that quickly.

blue underglaze, wiped blue underglaze and raw red underglaze on three sections of one pod
Alas, I had to be the one to change the color. Once all the blue was dry, I grabbed a sponge and wiped away the blue in the same manner as the yellow, leaving the deep spaces of the sprig blue and the raised sections red.

close up view of wiped blue underglaze texture

I also added green to the purple interior/ends and wiped it away in the same fashion.

green and purple ends

The plan is to add a clear gloss glaze to all six pods and attach them to a rod once they have been fired. The group of pods will be raised up from a planter rather than laying on their sides as they are in my studio and in the kiln.

clearly the cat feels affection for my work

Monday, August 21, 2017

Chain Mugs

measuring the chain length before cleaning and trimming

At the start of the summer, I had this idea to make mugs with chains. They're totally impractical, but I wanted to try it anyway. I started these in June, then realized that something like a cookie jar would be better with a chain because it wouldn't need to be cleaned as often or heated. Too late. I threw and glazed mugs, not cookie jars.

thrown mugs from June

These particular mugs progressed slowly, though. I threw and trimmed them in a couple of days, then took ages to get them glazed. I threw them as straight walled forms, then pressed the chains into the wet clay as I wrapped it around the mug, gradually moving from top to bottom.

chain mug with sprigs and cut groove

On two of the mugs I carved out a slight indent for the chain and added sprigs for texture. For the others, I wrapped the chain around the mug and gently pressed the soft wall of the mug out to bulge between the loops of chain.

chain mug with bulging wall

I fired all four mugs to cone 6 so they'd be food safe, using some new to me glazes. Since I don't fire cone 6 as often as I fire to lower temperatures, it took a while to fill that kiln.

bike chain before and after cleaning

Once the mugs were glazed and fired, I cleaned and prepared the chains. I started by cleaning them in Simple Green with a stiff dishwashing brush, then I used a spinning wire brush to clean off rust and the remaining oil. Strangely, one of chains didn't get completely clean using this method and I can't quite quite figure out why. It looks as clean as the others, but leaves grease on my fingertips.

using a wire wheel to clean chain

After the bike chains were cleaned, I used a chain tool to trim the chain to the correct length. This chain tool can be used to remove a link from a chain, cutting it down to size. It can also be used, with some frustration, to add a link to a chain. 

chain tool for removing or adding links

Once I had cleaned, measured, and trimmed the chains to size, I used two-part epoxy to attach the chains. 

mug, cleaned chain, and chain tool

I started with PC-11, but didn't feel like I was getting a strong bond and didn't like the white residue left by the epoxy, so I went to the hardware store in search of some clear epoxy. I hadn't used PC Clear before, but I've been happy with PC-7 and PC-11 in the past.

chain taped in place for epoxy curing

Both of the epoxies I tried are slow curing, so I taped the chains on the mugs for 24 hours. The chains fit fairly well in their grooves, but I wish I had made the grooves a bit deeper. The chain adds some weight, obviously, so adding thickness to the walls might not make sense, but with a shallow groove for the chain, there is some wiggle room where the chain is placed.

the PC-11 didn't hold this chain in place

I used PC-11 on half of all the chains and then switched to PC Clear to finish each mug. The PC Clear is much less visible, allowing me to use more of it. It's texture is similar to the glazed surface of the mugs, helping to make it less visible agains the glazed surfaces. On one mug, the PC-11 didn't hold the chain in place at all, so I redid it with PC Clear.

finished mugs before clear coat

Another potential problem with these mugs is that the chains might rust, especially if they get wet from cleaning or humidity. To try to prevent rusting, I sprayed a clear coat on the chains. Obviously I don't want to drink from a clear coat, so I protected the interior, handle and other exposed clay with masking tape before I sprayed on the clear coat.

taped mugs ready for clear coat

The end result is what I wanted, even if what I wanted is kind of silly. Obviously I don't plan to sell these not-entirely-functional mugs, but I wanted to try combining a functional form with an industrial look. I am considering, if I do this in future, making the chain from clay as well. If the chain were clay, it could be used functionally and cleaned with less fuss, but I am afraid it would lose its industrial look.

finished blue bulge mug

The trouble with making the chain from clay is that the major material feature of the chain is that it is thin and flexible in one direction while rigid and strong in the other. A clay chain that looks convincing would probably need to be made from separate cast or cut links put together on the wet pot. The small, thin pieces of clay would me more likely to chip, bend, have rough edges, or crack. Scoring and slipping might remain visible on the mug behind the chain. The final result might be more fragile, and, of course, the process would be quite tedious.

finished blue sprig mug

I was trying to envision using a 3D printer for the chain, but I'm not sure 3D clay printers can do such fine detail. If a resin printer is more detailed, it would still result in the same sorts of epoxy issues as the metal chain, but without the risk of rusting. A resin printed chain would look like resin, whereas with clay I could us gold or silver decal to make it look like metal.

finished colorful sprig mug