Jeff Longtin

I've had great success with Amaco Palladium Glaze on cone 6 slip cast porcelain. The vase pictured has 5 coats. (Thinned a tad from bottle thickness.) Fired cone 6 fast. (3 hours) Not quite a true mirror but a second firing, in a bisque or glaze firing, should change things up nicely.

Air circulation - I'll pick up on Bill's point - air circulation is only important in fossil fuel kilns: wood, propane, natural gas. As the fuel itself, creates an air flow, how you control this flow greatly affects your firing results. (How tall, or short, is your chimney / when do you open the damper, and how much, all affect air flow.) Electric kilns, for the most part, do not have "air flow". (At least to the same degree.) Making sure that no kiln shelf "blocks" an element is a good way to maintain heat gain but you're not really hampering any kind of "flow". (In electric kilns the heat is "radiating" not so much "flowing".) Several things affect how uniform a kiln will fire. One big element is tightness of the kiln pack. Leaving room around each pot/form allows air/heat to envelope it. This creates more uniform results.

Hello Sabi54. Nice link. The gal describes the process well. Two differences in my experience: 1) I let the mold purge a full 60 minutes at the end. (50-70 lbs. depending upon the pressure setting of the hydraulic press.) 2) I usually poured in a rigid mold casing made of steel or pvc. (That protected the molds from cracking when the press brought the two molds together.) Mold duct tubing - the first time I ordered it, without knowing its proper name, I called it "hollow cloth rope". If the rope highlighted, holds its round shape, then I think it might work.

Is this your first time working with wild clay? Typically, what settles out, IS NOT used. Instead, it's what stays suspended that's used. (After the excess water has been allowed to evaporate.) What settles out, seemingly wherever wild clay is processed, is fine sand. Once this has been separated out, the clay slurry is then screened to remove even more sand and debris. The slurry is then allowed to dry/stiffen. Its a tedious process but it is fun. (And it takes forever.) I dug up some clay in the back yard, in high school, and after a few washings I had a really nice "terra cota" colored clay. It didn't throw worth a darn but I made some sweet pinch pots with it.

Peter Pugger makes a de-airing hydraulic extruder that's very nice. Not cheap, and very heavy, but they make handles in no time. (The chamber is about 8" wide and 12" deep.) At the pottery shop they were used in the vertical position to extrude handles. They can also be mounted horizontally if that's your preference. (The pugmill actually mixes the clay, before extruding, while the extruder does not.) As far as maintaining the round shape I wonder if the tubes were extruded on to "half moon" shaped trays if they wouldn't retain their roundness? (Like baguette baking pans?)

Hello Jenni, If you're using a "cone 6" clay body you want to use a "cone 6" glaze. (Or "cone 5-6".) You do not want to use a low fire glaze on a pot that will be fired to cone 6. That is a recipe for disaster. (Glaze all over the kiln shelves, in other words.)

Hello Nata. Welcome to the Forum. Do you have access to Mason Stains? I find Delphinium Blue, at 2%, and Best Black, at 1%, result in a nice dark blue. (Anymore black and it overpowers the blue.) Vivid Blue, alone, is nice at 2-3%, for a deep blue, but not so "dark". (For that black is really necessary.) If you don't have access to Mason you can look up their ingredients and guess from there. (As they don't list percentages.)

Hello Phoenix, welcome to the Forum. Plaster is still the cheapest medium for slip cast molds.

When a kiln element looks rusty, the rings are close together, and the rings are leaning, you have an old element that needs replacement. (If the kiln is firing slowly.) If it's a relatively new element, relatively clean element, sometimes you can make this repair by gently pulling the element ends to lengthen them. Then weave the two ends of the element together. (Such that the two ends are in close contact with each other.) I did this on my Skutt 231 and the repair held for several years. While not ideal this repair did work when "supply chain issues" slowed down delivery of kiln parts. If the element has broken due to a small chunk of glaze landing on it, it's advisable to remove the discolored portion of the soft brick so it won't fuse to the new element and cause another break.

I recently worked at a pottery shop that had two of these beasts, made by RAM of course, and I can say they are quite useful production tools. Rather than use the provided 20"x20" metal "rings" we used custom made rings of 8" and 12" diameters. (Made by a local metal shop.) The 20x20 is a heavy form without cement but super heavy with cement. At least the 8 and 12 inch versions can be removed by a single person fairly easily. For the most part they're simple machines with simple hydraulic parts inside the cabinet. A bit challenging to find a repair person but if you're of the right frame of mind the normal "wear and tear" parts are easy to replace. I really think more colleges and universities should put these in their programs. Once you start working with them, and realize they're just another "tool", you realize they have lots of untapped potential.

Your elements look to be in great shape but your thermocouple is fried. I'd say start there.

That looks great. Congrats! A few other suggestions: I notice that your "keys" are small little bumps. With such a large mold its super easy to wear down small keys. (Unless you're very strong, gently positioning a heavy mold, is very difficult.) Once you start wearing down the keys it's difficult to align the mold parts. Instead think about making larger keys. (Mostly width wise.) Also, there's no reason a key needs to be a little round bump, in many factory photos I've seen keys that are raised shapes that simply accommodate the shape of the molded piece. (Think, for instance, the rings around Saturn.) If your keys were a raised ring form, around your round model, it would be super easy to set the top mold onto the bottom mold when you assemble them.

They make devices for smoothing wallpaper that are strips of aluminum with plastic handles that come in 12" and 24" widths. (with a straight edge of course) I use them to "screed" plaster forms. Run it on top of the set plaster, after 20 minutes, and you can get a very smooth surface.

Hello Califire, I'm not familiar with an "ammonite". What material is it made of? (Is it a shell or is it stone?) Murphy's only really works on porous surfaces, is the molded object porous? If I had been presented with this, I would have gone in the direction of a rubber mold, to get a plaster duplicate, and then start the molding process with the plaster duplicate. Whenever I cast something and it locks up the first pouring, I usually gently break the first casting and then add clay, as you describe, and then repour. Now that you know the piece is complex you might consider making it more than just a two piece mold. Also, that looks like a heavy mold, you might get yourself a tree saw and cut the corners off to lighten it up, (Tree saws are great for plaster.) Good luck

Good Morning Anna. Welcome to the Forum. Not really able to give you the answers you're looking for. Mixing your own would be the best way to adjust your recipe. I'm curious about an object that requires a 38 part mold. (Pictures?) As is, you're looking to change the clay to accommodate the mold, have you thought about the opposite, change the mold to accommodate the clay? (That's where I would start. Most production molds are in the 2 - 4 parts range. ) As you don't know the composition of the clays have you tried simply mixing them together? My guess is that any adjustment, to the Bone China clay, will result in reduced translucency, is that acceptable to you? Most Bone China objects I've seen were not made with complex molds but instead were made with several simple molds and many pieces were then assembled to make a complex form. Is that an option in your situation? Good luck