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Jeff Longtin

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About Jeff Longtin

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    Mold making, slip casting, porcelain,

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  1. For anyone wanting to create a large piece of plaster, with a smooth surface , I offer this suggestion: a tool known as a "paint guide" is a wonderful tool for a potter. (Essentially they're a scraper in a large format.) I have two in my studio, one that is 12" wide and another that is 24" wide. They are cheap, under $10, and they are stainless steel. (So they don't rust.) They feature a stainless steel strip of metal set into a plastic handle. I use them to give my plaster molds a smooth surface on their topside. (Such that the mold doesn't wobble on the pouring table.) They would als
  2. Typically people who want to make plastic dolls use molds made of urethane or silicone. Usually they might use resin to make the actual doll parts. Another medium, which I have not used, is called "composite". It appears to be a room temperature setting rubber- like compound. I've only seen it referenced a few times but I know that's a popular medium in the doll world. Artmolds.com might be a starting point for you.
  3. Yes, I distort porcelain castings all the time. (And then I remold them and create new forms.) I find cone 6 porcelain to accommodate this process quite nicely. Remember there are two types of cone 6 porcelain out there: one using Grolleg kaolin, nep sye and flint, and another using EPK and #6 Tile and maybe some ball clay?, and they have different workability qualities. The grolleg porcelain is a little more white but it is a little more short. (less plastic) While the EPK variety is a little more cream colored but a little more plastic. How well a clay serves your purposes really
  4. Yes, Morgan, Mason Stains vary vendor to vendor. (I've run into this myself.) The main reason, I suspect, is different batches. Laguna might sell a specific stain, rather quickly, and have a recent batch. The Ceramic Shop might not sell THAT particular stain, very much, so they're sitting on an older batch. While Mason tries to make sure each batch is the same their suppliers might have quality variations that they can't overcome? As a result different batches may appear to be slightly different. When you buy stain direct from Mason, 10lbs +, the boxes have the stain number and the
  5. I've been using cone 5-6 Porcelain slip for years and I really like it. I found 5-6 stoneware slip to take forever to set up. You seem to differentiate between 5-6 and porcelain, are you thinking about cone 10 porcelain slip? Years ago I mixed up a batch of the standard 25/4 recipe (25 kaolin, 25 Ball clay, 25 feldspar, 25 flint) and found the body to be very unfriendly to casting. You may have better luck though?
  6. The main reason you use a mold, to form a ceramic piece, is to reduce the effort necessary to make the piece. One impact, of the molding process, is that the cast piece will have a seam where the molds parts come together. If the seam, is placed well, the cleaning process will be minimal. If the seam is not placed well, the cleaning process will be time consuming, and the seam may be evident after cleaning. The form you picture may come out of a one piece mold but its hard to tell without seeing the form from the backside. per Chilly's comment about using a light. When customers hav
  7. I thin the glaze, Palladium, and I apply 4-5 coats. (By thinning it I can brush out the brush marks.) My work is slip cast cone 6 porcelain. I think the porcelain helps the glaze melt better and the smooth surface of the clay form contributes to the smooth surface of the glaze.
  8. Can you attach a picture? What kind of plaster?
  9. I've had great luck with the Palladium glaze from Amaco. I hoped I would have similar success with Saturation Gold. I did not. Every application looks like bronze. As Callie mentioned it is finicky however.
  10. Hey JF, There are two types of molding rubber: silicone and urethane. I have used urethane extensively. There is a local source for Polytek so that's the brand I have most experience with. 74-55 is a great rubber medium for block and case molds. (55 has some flexibility but keeps its shape. 30 is more flexible.) The advantage with urethanes is that you don't need to de-air. You get some bubbles but not enough to affect the molding surface. Jeweler friends use silicone but that's only because they pour hot wax into the molds and silicone stands up well to the heat. (Or so they tell me.)
  11. The vast array of colors they offered in the 80's and 90's were a combination of the colors they offer now. They refer to the new lineup as "base" colors. If you look at the "Archive Formulas" you will see the proportions they used to mix those older colors. The old Color Chart is nice because you can see an actual picture of the resulting color. (You can see the color, if you google it, but seeing an actual printed image is more what I'm used to.) Like most potters I threw mine away when it was replaced by the newer Color Chart. (Not realizing what a valuable resource it is when mixing
  12. In the 80's and 90's Mason Color sold 120+ Mason Stains. Their Color Chart was several pages long and was 8-1/2" x 11" tall in format. Does anyone have an old copy from this period? The newer charts only feature 60-70 colors and measure 6" x 11". Thanks Jeff Longtin Minneapolis
  13. A young coworker is an art history major. (with a ceramics minor) She told me her final paper was on this very subject, "Chinese porcelain." She explained that research suggests that the Chinese potters pre fired their cobalt oxide. They placed it in the front chamber, the cooler chamber, and fired it, thereby turning it into cobalt carbonate. We have both in the studio, so I'm aware of their physical differences, (pink vs blue/black) and aware that carbonate is slightly less effective, but not sure why they would have done this? (I've not had a chance to discuss THAT aspect with my coworker.)
  14. Thermocouples - I work with Skutt Kilns and L&L kilns. Skutt kiln thermocouples are exposed while L&L thermocouples are in a ceramic tube. (My kilns anyway.) The Davinci kilns have closed tubes while the E23 has an open end. You mention that your thermocouples are not in a tube. Can you provide a picture? A newer thermocouple looks like a metal rod bent into a "U" shape. An old thermocouple looks black on the end and has a mass of metal on the tip. As the thermocouple is the link between the kiln chamber and the controller its vital that they be in good condition. A thermo
  15. One nice feature of Zone Control is that it allows you to test amperage, on each section, easily and quickly. A simple command: Enter_diag_Enter_Amps_Enter activates a simple diagnostic. On a Skutt 1231PK I'm looking for 28-22-28. If those numbers don't appear it gives me an indication which section may be problematic. (Unfortunately with a 1231 there are three different element thicknesses so experience helps determine which element needs replacing.) If the numbers are below the ideal it tells me an element is old. If the numbers are higher than the ideal it tells me the wrong elem
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