Sunday, August 21, 2011

Some Finished Knobs, and a Report on the New Salt Kiln

Yes, I finally did fire some of those knobs that I was blogging about back in January and February. I have been busy with other clay projects, daily work at my nursery business, and with learning to use my new salt kiln.

As you may recall from previous posts, my other kiln was deteriorating badly and needed a rebuild. With the help of co-workers from my nursery who have worked as masons in Mexico, I designed and cast the firebox, door, and arch of my new kiln. The body of the kiln was built of hard brick, with a soft brick shell for insulation. There is a much better metal superstructure than was built for my previous kiln, thanks to my brother Don who is a great welder.

First the good news - the new kiln is vastly more efficient and faster firing. It will reach cone 10 in about 14 hours, and I think it will do even better as I learn to fire it. But after just 4 firings, the cast refractory arch will have to be broken out and replaced with a hard brick arch. We just did not cast it as thick as it should have been, and the stainless steel reinforcing rod was consequently laid in too close to the interior surface. In the very first firing with ware in place - there had been a s-l-o-w curing fire as specified by the manufacturer - the arch cracked right down the center, and debris sifted onto the pots on the top shelf.

It's apparent from the image how the rebar has broken through the refractory material. It's going to be a nasty piece of work breaking out that arch. I have the original arch form, a big tile saw with a new blade, and those same guys who built the cast arch to help out.

You can see below how I set a shelf in the top of the kiln to collect the crud that same down from the cracked arch.... better than spoiled pots. I was hoping to get one more firing before Art In The Pearl, but it is not too be - it was just too badly cracked after the last firing.

I did get some very nice pots from firing 4, and am looking forward to using the kiln once the new arch is in place. Sigh.....

Monday, May 16, 2011

Building a New Teapot Form...

I've been thinking about handbuilding some new teapot forms for my summer shows. I like to apply patterns to my clay while it's flat and helpless... much easier than individually incising whole pots. I also think that teapot users like the funky, vaguely irregular bodies of handbuilt teapots. And of course, I really like to make them - the only real reason to do anything.

I had thrown forms related to this quite a few times and knew the scale and proportion that I wanted to achieve.

First, the clay has to be conditioned to be at the correct stage of dryness for cutting, decorating, and building. I undress the block of clay the night before, and leave it out for 4 or 5 hours, depending on whether or not I have a fire in the studio. In summer, it takes much less time. I just want to be sure that the clay is stiff enough that it won't collapse when I start assembling my forms. It's also much easier to do the stamping, rolling, and other surface decoration when the clay is a bit firm.

The next morning, I cut the block of clay into 3 or 4 slices so it can dry further, and will be easier to put through the slab roller. I use Slab Mat paper so I don't have to remove any canvas texture from my work. If you don't have a big block cutter like the one in the image, there are still lots of ways to cut nice slabs. If they are going to go through a slab roller eventually, it doesn't even really matter.

Using a drafting compass, I create conic patterns for my teapot. I am using stiff sheet PVC for my patterns - permanent and durable for studio use. On the pattern pieces, I will record the name of the piece, how many pieces there are, and assign a number to each piece. That really helps for storage and retrieval. I have more than 100 different patterns floating around my studio. I do try to keep each one in a labelled zip lock bag.

Here's a little mock-up of what the form will be. This step is an essential part of pattern making - it will allow me to assess the scale and proportion before whacking into the clay. As you can see from the picture, I have already reduced the diameter of the finished piece a bit to conform to my internal vision of the teapot.

Pattern making in the clay studio is a skill that can be learned. I got a major head start on the process through decades of sewing practice, where I made most of my own clothing patterns. Any craft that requires estimation and visualization will help with pottery making....

Here are the finished body patterns, ready to cut. The clay is about 1/2 centimeter, or 3/16" thick.

In my next post, I'll decorate these two components, and assemble the body of the teapot. There's a previous post that goes into considerable detail around building a spout with a mandrell, so I won't revisit that step.

Monday, March 7, 2011

Deteriorating Salt Kiln Requires Rebuilding....

I've fired my salt kiln 77 times in the past five years. I thought in the early years that I might get 100 firings, but the condition of the kiln is beginning to concern me and it's clear that it's time to rebuild the kiln. This has been a problem kiln since I first completed it - lots of desire for the salt process but not enough knowledge to build the kiln properly. Basically, there's just too much hard brick in the kiln. There were a lot of stalled firings in the first year, and then I kinda got it figured out and was able to get it to Cone 10 in about 14 hours. Those were the good days.... sigh. But then, I changed propane suppliers and they changed the regulator on the tank, and a frustrating period began with terrible long firings that barely reached temperature. There was a lot of BAD SCIENCE on my part - and my need for work for shows and galleries kept me from doing anything serious to remedy the situation.

I might have gotten my 100 firings if it hadn't been for the many long stalls, hours and hours over 2000 F with temperature barely creeping up. You can see how damaged these bricks in the right rear of the kiln have become.
The skews in the arch are also deteriorating badly. I have been researching how much of the brick in my kiln can be reused - and I will be carefully evaluating each brick before I reuse it.

With new hard brick up around $7-8 each, I'd like to reuse as much as possible. I think that I will have to buy all new skews - they don't look good.

The kiln has steel angle iron edge pieces, but I am definitely going to use a wider stock in the new kiln. I am also going to offset the chimney so that a threaded rod can hold the back in compression at midpoint. You can see the rear burner pot - I will probably still have two opposed burners. I now have some really nice Buzzer burners that will be great for the new kiln.

You can see gaps between the bricks from movement of the kiln during firing. This is the left rear corner of the kiln, seen from behind. As you can see, there's some decent looking hardbrick on the outside of the kiln that should be reusable.

This is the middle of the left side of the kiln. In the first year or when I was really struggling to get temperature, I added a layer of kaowool insulation to each side under an aluminum panel. This location has had a lot of vapor escape, and it has really eaten up the angle iron reinforcement, and just plain dissolved the aluminum panel.

Here's another vapor leak on the other side. The kaowool is completely gone from that spot, it will be interesting to see what's under there.

I'm going to have some help with this project; a couple of guys who work with me are going to take the kiln down. I will sort and grind the brick... ooohhh! can't wait.

I'll post some more pix as I proceed, gotta have pots for Showcase!

Monday, February 7, 2011

Finishing up the Knobs...

Here are the blank knobs that were thrown at the wheel last week, with a little bit of incising added. I will probably make most of my knobs from low fire clay, especially those I need for my kitchen that will match my tile work there. I am sure that some of the knobs will find their way into the salt kiln, however.

These were thrown from my regular stoneware clay, but it really doesn't matter since all of these will perish in the press-mold making process.

Here is the freshly cast press mold, with 8 cavities for different knobs. The clay originals removed from the mold are scrap, and need to be dumped - not reclaimed - since they are contaminated with plaster scrapings. I will let the press mold dry for a day, and then clean it by vacuuming, and also by discarding the first knobs that might have plaster scraps in them.

I have found that the easiest way to get a consistently sized knob is to extrude 1" coil, and then cut it to specific lengths to get the size ball I want. I have also extruded 1/2" coil to use for the knob shanks, and have carefully cut it to 1/2" lengths. It's firming up as I press the sized balls into the mold cavities. I am going to throw a little tool to press the ball into the mold and mark the center of the knob blank. My clay (Georgie's Cannon Beach 10) joins to itself really well, so I just score the shank bit with a serrated rib and center it on the back of the blank knob. After the shaft is joined to the knob, I wait about 5 minutes and they can be lifted out with the shaft. Cool!

Here's a finished knob made from the first press mold. Since I have been just pressing sized balls into the mold, the deeper cavities of the first mold haven't been a problem. I'll probably touch it up a little bit with plastic steel wool or sandpaper, depending on what the surfaces are like coming out of the molding process.

When the knob has dried a bit, I use a drill bit to make a hole in the center of the shank. I am going to experiment a bit with this - perhaps using one of those angled hole cutters that are used to make teapot holes. The 1/2" shank bit would have to be dried to use a tool like that - we'll see.....

I have used a 5/16" drill bit to make the holes... I think that should be big enough after shrinkage.

Here's the finished knob that Ted Juve gave me with his first instructions. You can see how the brass sleeve sits in the drilled hole. Ted says that it is very important that the knob be placed right side up after adhesive is placed in the hole, and the brass sleeve is inserted. That way, the sleeve will be flush with the bottom edge of the drilled hole, and will not vanish into the knob if the hole is deeper than the brass bit. I believe he suggested that the gluing be done on waxed paper - that will allow the paper to be peeled away leaving a tidy knob, and no knobs stuck to the worktable.

The brass gizmos and their screws come from Aftosa.

Tuesday, February 1, 2011

Knobs, Continued.....

Here's a nice little trim chuck for trimming the knobs I made the other day. It has a broad surface to support the knobs, and adhere to them while they are trimmed.

It will make a pleasing small vase after it does service as a chuck.

I threw it on a bat, but did not cut under it with a wire. It's essential that chucks be perfectly centered so that you can make the most regular knob possible. I like for the clay to still be wet enough to still be slightly sticky when the chuck is used. That way, the object being trimmed stays put on the chuck, but it also means that it is really easy to ding up the top of the chuck. But if it is that soft, it can easily be touched up with a moist sponge after the trimming. Anyway, it's just a chuck.

I like little trim tools for operating on knobs, lids, or other small pieces. There's not much to cut away, and I feel like I have more control while trimming.

Here are my knobs, ready for some additional decoration. I'll do that tonight, and then cast them in plaster tomorrow.

You can see that all of them have had their sides angled in slightly to make for easy casting. I don't think that will detract from their finished appearance.

Monday, January 31, 2011

Making Handmade Ceramic Knobs

As many of you know, I have been making tile for my kitchen as part of a home remodel. Most of the tile is complete, and some is installed. In my dining area, there are beautiful new oak cabinets that will have a tile counter top and back splash. I want to make ceramic knobs for these cabinets. I first saw handmade ceramic knobs at the home of my potter friend Ted Juve, in Enterprise, Oregon. Ted explained to me exactly how to make them, and gave me a small bag of the threaded brass inserts that complete the knobs.

I made my first knobs about a month ago, and cast them in plaster to make a press mold, so that I could make as many as I needed. The first knobs I made were too deep, and had to be hand cut after forming. I decided to make a new batch to carve and cast in plaster, and include this fun process in my blog.

I started out to throw some new knob blanks off the hump with my regular stoneware clay. I brought up a narrow column of clay, and formed a small knob with my fingers that was about 2 inches across. I added a little dimension to it, based on which of the first knobs I liked. The idea is that these new knobs will be just about the size that I want the finished knobs to be, accounting for shrinkage, so that I can just cut the knob to the finished size with a wire while it is in the press mold. I plan to shape the sides of the knob blanks when I trim the knobs in a tiny chuck later in the process. This will eliminate any undercut that might complicate the plaster process.

You can see that I am cutting the the small knob off the hump of clay with a thread tool. This is a small bamboo knife - about 5 inches long - with a hole drilled in the rounded end. Then, a piece of stout linen thread (buttonhole twist from the fabric store also works....) is threaded through the hole and tied. I like about 6" of thread.

I use the bamboo clay knife to place the knob blank on a board to dry a bit for trimming.

These knobs are finished by adding a 1/2 inch plug of clay at the back, and drilling a hole about about 1/2 inch deep into the extension to make a shaft to receive a threaded brass sleeve after firing. This permits the knob to be attached to the cabinet door just like you attach those boring (and expensive!) knobs from the hardware store.

When these knobs have dried a bit, I will trim them and carve a little extra pattern into them. After that, I will join a section of extruded coil to the back to form the shaft. I am going to glaze these with the green lowfire glaze that I have used for my tile project, but also plan to finish some in the salt kiln.

Hmmmm........ that will be fun.