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Jeff Longtin

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Everything posted by Jeff Longtin

  1. The primary advice I would give you is be prepared to make mistakes. They happen. I've been doing this a long time and I still make mistakes. (Don't anticipate all the undercuts, don't find the right parting line, etc.) It's just part of the process. When I first started making molds, for profit, I marketed myself as "Complex Molds Made Easy." I made some very complex molds. (10 part was tops.) Most of those folks did not create businesses around the product. Many because complex molds are complex to use and complex to maintain. If possible, try to simply the form, such that you only need to make it a two - four part mold. This will be easier on you and easier to make the product easily and consistently. Thought to consider: only you know how complex the original form is. If you alter it, in some way, to make it easier to mold, the customer will not know. They'll only see the finished product, you present them, and appreciate what you have done. (They won't know you filled in 10 undercuts, instead of 5, like you preferred.) I always directed customers to Dept56 products for example. A wonderful example of a form that is highly simplified, to mold easily, and yet, when hand painted, given great complexity. Very few D56 collectors appreciate how simple the forms actually are. Good luck!
  2. Ani, To answer your question directly, Yes, molds have a limited number of uses. As Neil and Mark have stated, the clay you use, and how you maintain it, has the biggest affect on mold deterioration. The other aspect of mold deterioration is subjective, what you may find acceptable, and still usable, may be different then I, or the next person. One customer commissioned me to make 10 molds to replace her existing 10 molds. She told me they lasted thru 150 pours. I was astounded. She then explained that the pieces required a lot of cleanup. While the cleanup was time consuming she accepted the delay as she was unable to find a mold maker to replace them. She was overjoyed, when she found me, and overjoyed that she could finely replace her aging molds
  3. If the texture radiates out, uniformly, around the circumference of the form, the mold will likely "catch" along the edge. To minimize this I would suggest you fill in the texture, along the edge, with clay, before you pour plaster. I molded a similar object, many years ago, but I did not anticipate a problem. Unfortunately the texture "locked up" the plaster and I had to chip it off the piece. (The piece was in the bisque state, so there was no damage, but the process was tedious and very annoying.) After I judiciously filled in the texture, along the edge, I was able to pull a decent mold. You just have to decide how much texture loss is acceptable to you.
  4. As I craft forms from combined shapes I have many spheres in my studio. Acrylic tree ornaments come in a variety of sizes and mold easily. Bowling balls make great models. (Mold easily, don't distort.) Most bowling alleys have one or two chipped balls in the back room. 8.5" dia. exactly. You can also order "acrylic domes" from a variety of companies. (They're nice because they are seamless whereas the ornaments have a seam.) In a quaint part of Minneapolis they have street lights with plastic sphere diffusers. I checked with the grounds crew and they had a 12" and 22" inch diffuser in the back room. (Both with cracks however.) Those have been invaluable when I wanted to mold a large sphere form.
  5. If you include a picture, or send me a picture, I can offer advice. Dimensions as well.
  6. Reclaimed slip usually has enough deflocculant in it, already, that you don't have to add more. (Usually.) Such that I would suggest you not add more in the reclaim process. Reclaimed slip tends to have more water in it, than new slip, so I rarely use it alone. I usually add a bit to a batch of new slip. THEN, if the new batch seems overly thick I might add A LITTLE deflocculant, but usually not much.
  7. If you look at the website: ramprocess.com you will see the tabletop version. Looks like it goes for about 5K. An old model sits next to me, in case the big ones break down, and they are sweet little machines. The purge/vacuum aspect really expedites the pressing process. (You vacuum to suck the clay into the mold and purge to pop it out.) The 30 ton variety, in use, at work, are in use 6-7 hours a day. They allow for high production. I know a few studio potters who bought the 30 ton variety, thinking they'd make a fortune, but they're really not using them to their full potential. The tabletop variety is all most studio potters need. Repairing the things is a bit of a pain but the RAM folks are really great about walking me thru the process.
  8. At the pottery shop, where I work, we get "mask tested" once a year. A private company conducts the tests. About 8 people work with glaze materials so 8 people got tested. (I coordinated the event.) The mask test involves the tester putting a hood over the test subject and spraying a smelly substance under the hood. We look to the left, we look to the right. We look up, we look down. We bend forward, we lean back, All the while the tester is asking, "Can you smell that?" and then works with each test subject to make sure their mask fits tightly. They check our blood pressure and they note the brand of mask we are wearing. We wear the 3M brand Half Face Respirator. They fit well and can be worn several hours each day. We use the N95 paper filter inserts. The manufacturer recommends changing filters after 40 hours of use. A P95 filter can be used but its intended for "oil based" material and needs to be replaced more frequently.
  9. You have good air flow/purging so that's good. The design looks FAIRLY unobtrusive, so that's good. Thinking about it...the folks who use the presses, at the pottery shop, do allow their clay to stiffen. They are, however. using 30 ton presses. Can you use stiffer clay and pound it in using a hammer? (There's a video online showing such a process.) The RAM press also allows the user to throw the mold into vacuum. Does your device allow that? A drier surface could also help. Pure-Lube is described as a separating compound. (Like Murphy's Oil Soap.) It's typically used to separate plaster from plaster in the mold making process. If its working for Mark, great, but I would not recommend in this situation.
  10. I work at a pottery shop where we have a few RAM press machines. I make several air-release molds each day. (I go thru a lot of Ceramical.) Your situation seems odd? If you're getting air bubbles, with no clay, it should be able to express the tile out. Can you post a picture of the mold and the tile form? Are you getting air over the entire surface? Could it be that when you made the mold the air gate moved or wasn't held it place securely? When you mixed the Ceramical did you follow the instructions? USG suggests water at 77 degrees. At one point I used really cold water and that affected the purging. Are you using old Ceramical? All bags are dated. What is the date of yours?
  11. Without photos I'll make a few assumptions: more than likely the rim/lip of your bowl form is rounded. (correct?) Regardless of the angle of the wall, if the lip is rounded, that is likely where the form is "catching". Running a fettling tool, around the rim of the form, will remove the undercut. Then, with one hand in the bowl, holding it as best you can, pounding on the mold rim, with a rubber mallet, will loosen the plaster mold. You can do so with a steel hammer but that will damage the mold rim. Sometimes a gentle pounding releases a form immediately, sometimes it takes a few minutes, but either way, its the only method to encourage separation between a stubborn form and the plaster mold.
  12. 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 also come in handy if you're pouring a plaster wedging slab. Just run the tool across the surface of the setting plaster and you will have a nice smooth surface upon which to wedge your clay.
  13. 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.
  14. 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 depends upon what you intend to do and your skill level. All clays have challenges. How you adapt to these challenges is really the key.
  15. 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 batch year. While you might not be buying stains at that level, more than likely Laguna and Ceramic Shop are, and you can ask them the batch dates. If they differ that's probably why the colors differ.
  16. 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?
  17. 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 have a hard time envisioning where the seam might be I suggest they do the same. In a darkened room turn on one light source. Take a pencil, and draw a line, where the shadow ends, on the piece, What this tells you is everything that is up to that pencil line, will "pull" in that direction. Anything that is in shadow, on that side, is undercut and needs to be filled in. You can then turn the piece so one shadow lines meets the edge of the next shadow. Then draw another line and this will show you the parting line of the second piece. By hiding the seams well you make the cleanup process a breeze. The quicker a person, can clean a clay object, the less time they have to handle the clay object. The less time they handle the object, the less chance they have, of deforming it/distorting it in anyway. A little abstract but the basic idea behind good mold design.
  18. 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.
  19. Can you attach a picture? What kind of plaster?
  20. 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.
  21. 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.) Plus urethane is not as expensive. In the 80's Donald Frith wrote a book about mold making, "Mold Making for Ceramics". It's a very good book. In it he mentions/recommends Smooth-On. Upon reading this I called Smooth-On and they were kind enough to send me some samples. (I told them I was just starting out as a mold maker.) They're urethane products are similar to Polytek, but Polytek has a local rep, so I have stuck with them over the years. Shelf life - the manufacturers usually recommend a shelf life of six months to one year. While that's ideal I have had urethane left over, from a project, that has sat on the shelf for several years. Old urethane seems to capture air bubbles more easily, and it has a nasty smell, but it has worked for simple forms. (Forms with smooth surfaces without detail) A trick is to put leftover urethane into smaller containers with little room for air. fyi- I only use old rubber for my projects. I buy new when I start a new project for a client.
  22. 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 new colors.)
  23. 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
  24. 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.)
  25. 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 thermocouple can become dysfunctional for a variety of reasons. Age is one. Sometimes glaze will fall onto the tip and affect its ability to read temperature correctly? Sometimes a kiln is packed tightly, around the thermocouple, and that will affect its functioning? I've spoken with Rob many times and he's a terrific resource. Usually he's been able to solve my problems. Have you used a meter yet? That can greatly aid the process.
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