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Everything posted by dom92

  1. I had an odd failure happen yesterday, and I'm not exactly sure what to make of it. I had used a premixed ^6 porcelain slip to cast a small coffee cup in a plaster mold. The label on the slip container states: Glaze fire at Cone 6 - 2232 F Bisque fire at Cone 04 - 1940 F The kiln I used was manual, so I slowly (over about 8 hours) brought the piece up to 1940 F and held it for about 15 minutes, then let it cool on its own in the kiln over the next 12 hours. Everything seemed successful. I then applied some Cone 6 glaze and then, over several hours, brought the kiln up to 2232 F. When I opened up the kiln the next morning I was shocked to find my cup a melted blob on the floor of the kiln. It was like it turned to lava sometime during glaze firing and just completely collapsed. What's odd is this failure came at the end of successfully making 3 other cups using the precise same steps and the same slip. I'm of course hesitant to try to make any others until I figure out what happened here. I'm thinking of several possibilities: - My pyrometer is off and I didn't actually get it up to proper bisque temperature - Bisque temperature was fine but I didn't hold it long enough - Ramped it up too fast during glaze firing (I have an electronic sitter but haven't hooked it up yet) - A problem with the slip itself (which I think is unlikely since it's from a well known local manufacturer and since I've had 3 previously successful firing/glazing) And of course there could be something more simple I'm missing here. I'm open to any suggestions.
  2. I'll pick up some cones the next time I'm at the store. Until now I've hesitated on using them because my Skutt kiln has no spy hole. The only way I'd have to check a cone would be to open the kiln, and I like to avoid doing that so I don't cause unneeded stress to the piece I'm firing.
  3. The entire setup is a K2 Instruments model DP-902F. The thermocouple end is just two wires twisted together with a dab of what looks like solder connecting them. The K type thermocouple I ordered to replace it was this: https://www.amazon.com/gp/product/B00XJ0VUBG/ref=od_aui_detailpages00?ie=UTF8&psc=1 A totally encapsulated thermocouple. Definitely different than what I have now.
  4. Okay, everyone, I think I discovered the obvious problem. I was following up on neilestrick's last post and looked at the manual again. I clearly misread things before. The pyrometer itself has a max temperature of 2372 F, but the thermocouple that came with it is only rated to 1500 F. I would presume that trying to fire the thermocouple some 700 degrees above its max rating could cause some readout accuracy issues. I'm an idiot. I've already got a high temp (2372 F rated) thermocouple on order and it'll be here on Saturday. I'll hold off subsequent firings until then. I appreciate everyone's patient replies and advice.
  5. I have no other slip in my possession right now, so there's no way I could have confused it or taken from the wrong container. Here's a photo of the actual label: https://drive.google.com/open?id=1jhW5ELUxn14f38kONTrtvVy80RyG7WB0 I don't have any "program" as my kiln is fully manual with a limitless switch. I discovered one new potential problem since my original post when I pulled out the manual for my kiln today. It notes that the pyrometer is not rated for temperatures above 2000 F and that if kiln temperature is raised above 2000 the pyrometer *may* show an error code until temperature drops below 2000. My pyrometer went up to 2232 F just fine, but now that I know that's above its rated temp I'm wondering if what I was seeing was completely inaccurate? I'm also wondering if this was as simple as not stirring up the slip well enough before pouring. Sometimes I'm not as diligent with that as I should be.
  6. Unfortunately all of my other bisque from the same slip has already been glazed. I'm measuring temperature by using the electronic pyrometer that came with my kiln.
  7. I didn't have any actual cones in the kiln. After this I recognize I need to pick some up next time I'm at the ceramics store. I'm wondering about the kiln overfiring as well, like perhaps the pyrometer malfunctioned. It didn't seem to be porous after bisque firing. I put some water in the cup for awhile to check for leaks or seepage and there didn't appear to be any.
  8. It's hard to say because it melted in to such a messy blob. The parts that were still identifiable did appear to have glazed just fine. There's no chance I used the wrong slip in this case. One other possibility I was just thinking of. Could this could occur if I didn't stir/mix the liquid slip enough before casting?
  9. Do the experts here have any sage advice on the best plaster materials to use for making a good slip casting mold? Until now I've used a wide variety of commercially produced slip casting molds and they've all been excellent in quality and construction. Nice rounded edges and very durable. I've even dropped a few here and there and all they did was leave a dent in my vinyl floor. Anyway, this weekend I wanted to take a shot at making my own slip casting mold using plain old plaster of paris bought from the local hardware store. It "works," but I can already tell this won't hold up for long. One drop, even to countertop level, and it'll probably explode in to a dozen pieces. I'm thinking this primarily due to the type of plaster I used to make it. Do the commercially produced molds use a different kind of plaster? I do have a bag of jewelry casting investment (which is primarily POP), and I was thinking of giving that a try as I know from experience how smooth and durable it is. I just don't know if it will absorb water from slip properly.
  10. Thanks, Fred! I should have guessed that there was a special mix out there. I'll give it a try!
  11. I've looked thru the instruction manual they sent me and operation definitely seems within my learning curve, especially considering it's pre-programmed
  12. Hi All - I've been using a fully manual kiln for awhile now, but have experience in the past using PID controllers. I finally decided to upgrade my current manual kiln with a new PID controller. It arrived today. The problem is that the instruction manual has left my completely dumbfounded. It's like it's written in Old English. http://www.thermomart.com/download/PID-DTXG.pdf I don't recall my old PID controlled kilns being so complicated. I think perhaps their instructions were extremely dumbed down for laymen and that's why I had no problems with them. But this reads like an engineering manual to me (which means I'll likely never be able to get the thing turned on, let alone program it for a few simple ramps and holds). So I'm not necessarily looking for anyone to help me decipher this, but I was hoping somebody could at least point me to a simplified set of instructions for such a PID or perhaps a YouTube video. I've found this particular controller in a few videos already and all people say is "this is an extremely difficult controller to program. Read the instructions carefully." That's not much help when I can't read them.
  13. They say it will work fine. I indeed have a small kiln, 15 amps.
  14. I ended up going with this one: https://www.ebay.com/itm/Kiln-temperature-controller-PRE-PPROGRAMED-PMC-metal-clay-beads-fusing-enamel/401330421128?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 Similar sort of PID controller, but completely pre-programmed and can also be customized. Most importantly, I had the manufacturer send me a copy of their manual and it's definitely something I can understand. I've heard of the Orton controllers, and I've actually used similar ones myself. Definitely easy to use. I just didn't want to spend that much right now so was looking for a less expensive option.
  15. Thanks, Neil. I finally decided to simply return the controller after reading a similar post from a different forum where people said, "at all costs, avoid PID controllers that need to be programmed." I instead ordered a new controller (just slightly more expensive) that's completely pre-programmed and also comes with a laymen's guide manual that I can understand.
  16. Hi All - New to the forum but not new to ceramics. I've got a strange problem I'm hoping somebody here can help with. For several years now I've been using a locally purchased Porcelain ^6 slip to make coffee cups and mugs in two part slip molds. My normal workflow was to pour the slip, wait about 15 minutes, then pour off the excess. After about 2 hours or so I'd open up the mold and pop out the object to let it air dry. These steps have worked well and I've never had any problems to speak of. Yesterday I went to the shop to get some more slip and they advised they had discontinued my favorite product. They recommended what they said was an almost identical Porcelain ^6 slip, except this stuff was "translucent." I thought I'd give it a try. The problem is there is clearly something very different with this slip that has thus far made it impossible for me to get objects out of the two part mold. I tried my normal workflow and everything went fine until I tried to open the mold after 2 hours. The cup split in half down the mold seam when I opened it. Minor glitch, I thought. I tried another one but then let it sit for 4 hours before trying to open the mold. This one split down the mold seam as well. So right before bed last night I tried one last time and decided to let the mold sit overnight before opening. When I awoke this morning I'd found the clay had dried enough it was starting to pull away from the sides of the mold but now there was a 2" crack extending down from the lip of the cup. Clearly this new clay doesn't like me. I must be missing something here. I've never used a "translucent" slip before, so maybe I'm making a major mistake in my workflow I'm not seeing. I'd appreciate any advice others may have.
  17. They've stopped making it in any quantities that are useful to me. I only buy my slip in 1 gallon jugs because it'll take me 6 months to a year use it. I believe they said I could still get it in 5 buckets, but I thought that was simply too much to deal with. Not only in having a single batch of slip sitting around for years but also just in having to heft that thing around. Given the problems I'm having with this new slip, however, I may need to reconsider things. My local ceramic supply store is pretty big and provides the materials to most of the local craft shops and studios in our metro area. All the clay materials they sell they make themselves.
  18. I appreciate the advice, everyone. It's definitely something about the chemistry of the new slip. I scrounged up enough of the old slip from some used barrels to make another pour. It turned out perfectly, just like it always has. I may give the vinegar fix a try and see what happens.

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