Jeff Longtin

The process of layering glazes is how you achieve an "iridescent" quality. Layering a stiff glaze, on top of a runny glaze, or vice versa, is the way to add complexity to your glazes. The Amaco Potters Choice glaze page shows some examples of such combinations. The one bummer, which requires testing, is that the runny glaze may run too much and you have glaze on the shelf.

The pottery shop most associated with this process is Dock 6. Kerry Brooks is the potter and she applied this process to coasters as well. She spent a year, or two, developing the process and the glazes that go with it. Again, she spent a year, OR TWO, developing this and I know she had a lot of failures. (Her studio/shop is a few miles from mine. I know she experimented with glazes, with firing temperatures, and with types of glass.) Once she found success technically she found success in the marketplace. (Anthroplogie ordered 1000's.) Having seen failed experiments with coke bottles, in high school and college, I have never felt inclined to attempt anything like this. She found the sweet spot and her coasters really are a thing of beauty.

A few years ago I was replacing a brace, on one of our glaze kilns, and my drill bit was dull. My boss brought it to my attention that a small nail easily punctures stainless steel. Turns out he was right. You don't want to pound the hell out of it but a gentle strike, with a hammer, does the trick. (And make sure the nail is sharp.)

The environment you fire in has no bearing on the glaze surface. Matte glazes are possible in both gas and electric kilns. Dumping alumina hydrate in a glaze, up to 5%, will turn most glossy glazes into matte glazes. (Or some variation thereof.) Changing your clay or silica percentage is the ideal way to do it however. Digitalfire.com has a load of glaze recipes and talks about this in detail.

Years ago, on another pottery blog, Clayart, someone mention that English potteries use "tongs" that are essentially strips of wire, extending from several fingers, that hold plates along the edge. The idea that holding the plate, along the edge, creates fewer noticable glaze tong marks, seemed like a good idea, to me. However, crafting wire in such a way that it could hold a plate firmly seemed challenging. So this is my alternative solution. My original thought was to use cookie cutters, thin strips of steel in other words, but I couldn't find cookie cutters that were big enough to hold a plate. Looking around my living space I saw a jar cover and thought it might work. Turns out these work really well. I need to grab the plate firmly, before I dip, but otherwise they hold 12" plates nicely.

Welcome to the forum Allison. I own a 231. I bought it in 1995 and it fired well for 25 years with the original elements. (I presume they were original?) I replaced all the elements last year and now it fires to cone 6 in 2.5 hours. (Half load.) I did spend about $400 dollars on 6 elements but it was worth it. The kiln has three sections and a top and a bottom. More than likely the top section was separated from the others and set down on the ground. It was not done so carefully and the bricks were damaged as a result. Replacing brick is tedious but not impossible. (You loosen the bands, holding the steel casing tight, and then you gently pull out the damaged brick.) Its not easy, and requires a "gentle but firm" touch, but it can be done. A better picture would tell us how damaged the interior is. My guess is that the school did not use it that often and that the brick, outside of the damaged brick, is probably in good shape. (The brick, at the top of the kiln, has little discoloration. That suggests they propbably didn't fire often or didn't fire highly volatile glazes.) A Skutt tech told me they stopped making the 231 in 1975 and no longer kept production records. What that means is that parts are harder to acquire. I would call your closest pottery supplier and see if they carry replacement parts for such kilns. If that seems doubtful I would agree with Neil and look at a newer kiln instead.

Here are plate tongs made from plastic jar covers. (For some reason the image is sideways?) The many holes prevent the lids from holding glaze which then drips onto your still wet plate. The little notches in the lid rim aid in holding the plate edge. Once the glaze is dry I dab a little glaze where the lids held the edge. Generally speaking it enables me to glaze plates without any drip marks. Really appreciated with translucent glazes.

I'll explain it this way: the choice between various kilns has a lot to do with the appearance you want you work to have. The type of fuel you chose to use will affect the appearance of your work. Electric kilns fire oxidation and mostly create a "neutral" atmosphere. That means glazes colored with stains mostly. Cone 6 is the popular "electric" temperature. Electric kilns are great for porcelain because the clean atmosphere maintains a white clay. The second type of fuel that is often used is either natural gas or propane. (Propane tanks if you don't have a gas line nearby.) Natural gas/propane allows you to reduce the atmosphere and bring out warm colors in stoneware and porcelain clays and glazes. Celadons and tenmoku glazes look best in reduction atmospheres. Wood is the third fuel and its a lot of work. Like the gas fuels it allows you to reduce the atmosphere and get beautiful warm colors. As electricity is a newer invention most of the world's beautiful "ancient" pots were fired in wood. If you want a kiln that is easy to set up in a basement or garage, and can be moved easily at a later date, then an electric kiln is a good choice. If you are in a more rural setting and have room for such things, outdoors in a kiln shed, a gas/wood kiln is a nice choice.

To expand on Kswans point: my guess is that you took three round tubes and set them on a table and draped the clay slab over them? I would suggest you make three clay tubes the same diamter as the tubes you started with and fire the slab on them. Where the slab touches the clay tubes will need to remain unglazed, and the tubes would need to be kiln washed but this would give you the support you're missing. I would close off the ends of the clay tubes to prevent them from collapsing as well.

To pick up on Min's point: you are aware that they make "kits" that are essentially rubber molds that enable you to press cookie dough into them and bake your own gingerbread house? A simple option would be to make a plaster mold of the plastic/rubber kit (positive) and then make another plaster mold (negative) to repoduce the plastic tray in plaster form. Then use this plaster form as a press mold for clay. Have you ever heard of alginate? Essentially its a gelatin like product that is skin safe. The nice thing about it is that it doen't get hot. You would still need to seal your current house form but the alginate would allow you to mold the form as is. (without too much concern for undercuts) Once molded you would need to make a plaster form and then a plaster mold BUT you can, at least, get a nice mold of the form as is. To pick up on Mark's point however: even if you can find a way to mold the thing with undercuts you still need to keep in mind that when you pull the clay out of the mold the undercuts will tear the clay. Therefore its best to reduce/eliminate undercuts, as much as possible, so the clay pulls away easily.

My trick for glazing plates: grip the plate by the edge and dip it into a large flat pan of glaze. Near drippless glaze application. (With slight touch up along edge.) I take plastic jar lids, peanut butter lids are great, and drill holes into them. Then I cut little teeth into the edge. (If you don't drill the holes the lid captures glaze which will drip onto the plate when you turn it upright. The little teeth hold the lip of the plate securely as you move the plate around.) Plastic kitty litter trays make great glaze pans for plates. I have several sizes in the studio for different sized plates.

Hey Min, Interesting conversation. I only cast earthenware in the 80's when I just started out. Minnesota Clay mix. Having craze issues I soon moved to stoneware, Duncan. (rumored to have been "Bmix") and then to my own mix of cone 6 porcelain. (Dorothy Hafner) Coincidentally my studio neighbor just bought a 100lbs of something called, "Zero4". I was just reading up on it before I saw this posting. Good Luck High Bridge. Great to see you taking this on.

Welcome to the Forum l.mourad6663. The simple answer, to your question, is Yes. The percent of "concentration" is the big question. Are you mixing your own clay? Do you have a recipe you can post? If you're starting from scratch there will be a certain amount of trial and error to get the right percentage of sodium silicate. The actual percentage you use will be quite small, compared to the overall proportions of the entire mixture, but a little, one way or the other, will have a big impact.

Did you do a Google search on the kiln? It looks like it was manufactured by Ceramic Fiber Fabrication (CFF) which became Keithcompany.com. It looks like they are an industrial kiln manufacturer out of California. (BIG kilns in other words.) Interesting website. They might have some information?

I've had to make this repair a few times. (per Neil's link) The ribbon is surprisingly delicate but the repair is very easy and effective.

To pick up on Rae's point: changing the bisque temp can sometimes greatly affect the absorption of your bisque pots. This, in turn, will then affect how your glaze is absorbed and, in turn , affect how your glazes turn out. If your problem glaze is just one or two, of many, then its best to go after recipe and not temp. If your problems are across the board, affecting all glazes in other words, then such changes may be warranted.

To clarify: in this photo we see "blistering". In your previous posting we see "pinholing". Blistering is when gas bubbles rise through the glaze, when the glaze is molten, and pop open. (And then the glaze cools before the blister can smooth over. ) While pinholes leave little holes, that are visually unappealing, blisters leaves sharp edges, that scratch the skin. Unfortunately it requires several tests to solve both problems. (As suggested in the previous post.)

Mason Stains - Ceramic Supply Pittsburgh Mason makes a Color Chart and it lists the recommended percentages for each stain. The only place I've found it is provided above. It's quite useful. It also lists the recommended amount of zircopax to use.

We use Potters Pads, from MN Clay, regularly at the pottery shop where I work. One trick, I found, was to moisten the bisque surface before stamping. That seems to give a much sharper image.

To pick up on Neil's point: I have lots of PVC piping in the studio. I use it as a base for several forms. A size I found useful was the 3.5" diameter tube. I made a mold of it and its the basis of my braille cup form. With a cone 6 porcelain, 12% shrinkage, it fires out to a nice 3" diameter. Another useful size is 4.5". During the summer I had an idea, for a new form, and bought a bunch of 1" x 10' tubes. When I brought it back to the studio I found it did not match my previous PVC tubes. It was then that I learned that there are several types of PVC tubing. The tubing in question is referred to as "Charlotte pipe". Turns out its 4" pipe is actually 4.25" O.D. and makes a great base for a large diameter mug form. (I think the 4.5" standard PVC is just a tad too big.)

Yes, Rae. I usually lay the grids on top of 1"x1" or 2"x4" strips for that reason. Especially fresh plaster. For porcelain platters I find it's not necessary to provide that much circulation. Simply putting the grids on plywood bats works well in that situation.

As its comes up in the past, on occasion, I will mention a tool I use in the studio that is quite helpful. Plastic grid light diffusers. When I first started making molds I was surprised to find that freshly poured plaster emits a lot of moisture as it drys. My first attempts to provide a flat drying surface, 3/4" plywood, resulted in complete disasters. (As the plaster dried it dampened the wood. As a result the wood warped. As the wood warped so did the plaster. Completely ruined the plaster forms I was making at the time.) A few days later, while at my day job, (maintaining a 26 story building) I replaced some overhead light diffusers in the freight elevator. Noticing that they were rigid I took them into the studio and tested them as drying surfaces. They're perfect. They're stiff so they don't warp. And they're plastic so they don't absorb any moisture from plaster or clay forms. The ones that work best are made of square grids that have hollow spaces in middle. Down side is that they have little burrs, every so often, so one needs to be careful when drying clay pots on them.

Welcome to the Forum Johnny. What you have is a slip casting tank/pouring table. The parts are very simple mechanical parts. You may be able to find replacements at a Home Depot type store. The motors are standard Dayton motors available through Graingers. (The tank/table itself is fairly unique and not easy to find a replacement for it.) To what degree you clean them, and use them, or buy new, is up to you. The market for tank/pouring tables is mostly a thing of the past. As a result they are much more expensive than they used to be. Cleaning what you have, and seeing how well it works, would be a good first step. When I first started casting, in the 80's, I was strongly encouraged to buy a casting/pouring table. I thought the design seemed logical enough so I was excited to cast up 1000's of pots. I soon found the design not so ideal. As I filled the table with molds at some point I chipped a few and plaster chunks fell into the slip. That was annoying. Then I found that the little bits of hard clay that were left over, after draining the molds, would fall into the slip tank and need to be screened out. (as with the plaster.) I found that time consuming and inefficient. In the end I found it easier to pour the slip into the slip tank and drain the mold away from the tank. Once the initial amount of slip is emptied out the mold is set aside and the remaining drainage is simply discarded. (In case plaster chips, and other stuff, contaminate it.) Good Luck

Years ago I worked with a potter who was using Domestic porcelain with nylon fiber. Thinking it would solve my warpage problem I decided to add nylon fiber to my cone 6 porcelain casting body. Other than making the slip thicker it really didn't affect usability all that much. (It also didn't improve warpage, on my larger flat forms, so I abandoned the practice.) An alternative for you might be using hemp fiber. I am in agreement with others, however, and think you might have better luck developing a flameware body, and adjusting it into a casting body, rather than thinking about fiber alone.

Soft soap works well to seal plaster surfaces, it's not as effective, when sealing fired/vitreous surfaces. (But it can help to provide a "release".) If I'm in a situation where I need the form to survive and I'm unsure how vitreous/porous it is I will often apply a thin coat of vaseline. That way I know I'm applying a protective layer that should prevent sticking.