Jeff Longtin

Hello Bristol Potter. Yes, I cast porcelain and stoneware. (Porcelain in my studio and stoneware at the pottery shop.) I don't mix stoneware from scratch but I do mix it from premix powder. (Laguna B-Mix.) Your comment about SG left me puzzled so I held off replying initially. The premix has all FOUR deflocculants in it. Darvan, sodium silicate, soda ash, and barium carbonate. Not a combination I've ever used but it does work. It's been a bit of trial and error but I finally got it down so we have a SG of 1.75. The flow, thru a Ford cup, is about 40 seconds. Lagunaclay.com has several recipes you might look at. (Go to More than go to Clay Resources.) There you will find several variants using the above combination. It sounds like you have your own clay body but at least you might try some of the deflocculant combinations they suggest? Good Luck!

A simple way to find out if its your water...go into the bathroom and lift the lid on the toilet tank. More than likely the tank has a ring of some color. (Brown means you have iron in your water and blue green means you have something else?) If the tank water ring matches your butter dish ring I would presume its just a water issue. (Minerals in the water in other words.)

I'll put in a second for the Fred Olsen Kiln Book. His little Fast Fire kiln is easy to build and easy to fire. Plus, it's not too big, 10 cu ft. I helped build one years ago at the MN Ren Festival. Two fire boxes are a little tedious but it made it super easy to control. Usually got to cone 7 just as the Festival was closing. (Once people were gone we'd throw in salt.)

Thanks for posting this Mark. I'm a big fan of all things art related and the California scene. In the 70's/80's the work of Ken Price was getting lots of attention and it drew my attention to what was going on. Also in the 70's, when I was in high school, my mom worked with a gal who had lived next door to Gertrude and Otto Natzler. (And helped them in their studio.) When she found out I was a potter-in-training she gave me all her tools and showed me her collection of their work. Only afterwards did I do some research and found out just what amazing glazes they created.

Thanks Dylan! It's called Amaco Brush-n-Leaf Liquid metallic - Interior Gold Leaf. A little smelly on application but fine the next day. Unfortunately Continental Clay is discontinuing it so I then tried the Craftsmart product. Looks to be about the same.

Thank you Hulk. I knew that differing temperatures can affect HOW water behaves in a mixture, like mixing plaster for instance, I just didn't know its actually quantifiable. It just dawned on me I could also buy some distilled water and see how that measures?

To update: I mentioned my interest to an artist friend and he explained that there are two types of gold leaf: the real thing, expensive, and the imitation version, not so expensive. He also explained that applying gold leaf is very difficult and he would not recommend it. He said the better paints do a good job of creating a similar effect. Turns out Amaco makes a non fire gold leaf paint. Maybe not as durable as gold lustre but alot easier on the lungs and studio.

I've been assigned a new task at the pottery shop: mixing casting slip. As I'm making 20 gallons a day I'm using plastic buckets to measure water. I tested several buckets and noticed they all differ, slightly, in what they consider "one gallon". I decide to stick with one bucket to keep things consistent. I then consider measuring deflocculant. There too I notice several different plastic things measure out milliliters/ounces differently. So I wonder: does the "weight of water" still hold true that one gram of water, by weight, equals one milliliter of water, by volumn? If this holds true then all of my plastic measuring devices are incorrect. (Only slightly, though, but incorrect nonetheless.)

A few slip cast issues to consider: as slip cast pots tend to be cast thinner than hand built/wheel thrown pots, most folks wait until the pot is bone dry to clean them. "Underglazes" tend to have more non clay ingredients, in them, so they partner better with bone dry pots. "Engobes", which tend to have more clay in them, tend to work better when applied to leather hard pots. Which you chose would depend upon when you intend to apply them to the pot/ceramic object. Underglazes and such aren't really designated "stoneware" or "porcelain" instead they're labelled by the temperature they commonly fire to. As Neil states, however, many/most underglazes can go to cone 6. The only issue that really has relevance is whether the underglaze color remains strong at the higher temperature. Many colors fade, as the temperature climbs, so testing is best. I just looked at the Witgert website. It looks like they make several types of clay for the ceramic world. The fact that your clays are from the same producer, is a good sign, but the fact that they make so many types it will require you to run tests with the actual clays you have.

Another thought comes to mind...how long, and how aggressively, you mix the plaster also affects its strength. (This is another reason why proper water amounts are important.) My mix time for plaster is two minutes soak, two minutes mix, and one minute sit. If the plaster is still fluid I will continue mixing, for a minute or two, until I reach a "melted ice cream" consistency. You know you're not mixing well enough if a slight layer of water appears on the surface of the setting plaster.

Truth be told Kakes you are exactly a "typical ceramic artist". No need to apologize. The major ceramic companies, Duncan and Amaco, designed their product lines to serve customers just like you. The ceramic choices at 06-04 are much more diverse than the choices at cone 6/10. I work with a number of young people, recent ceramic grads, who are not concerned with durability or process but instead with simply making "interesting/unique" ceramic objects. I applaud their ambition as I applaud yours. Your results may not be, exactly what you want them to be, but if you lower your expectations a notch you will find some amazing results nonetheless.

One question jumps to mind: are you using the proper amount of water or "as little as possible"? Most casting plasters, I think, use 35-40% water. Do you have access to "pottery plasters"? Casting plasters, from my knowledge, have hardeners which make them more durable than pottery plasters but also less absorbent. If my memory serves me correctly there are three kinds of "plaster"; pottery plaster - for casting ceramic objects, gypsum cement - harder than pottery plaster but still absorbent, for machine pressing of ceramic objects, and casting plaster - designed for the giftware industry for very hard plaster objects which take paint well. Does your source differentiate between the three? Clay - without deflocculant you need to add more water than is necessary. Have you tried using a deflocculant? In theory your clay has no elements that are antagonistic to the molds but it could be your clay does have things in it that are not friendly to your plaster molds. Those unknowns could be causing early deterioration?

Sweet pics. My studio is on the third floor of a six story warehouse. While I don't have pets, myself, several neighbors do. Little Bella, a Weiner dog, will stop in and say hello. The other neighbors like to hold her in their laps, when she visits, but I don't, so she sometimes gives me a disapproving look. Leo, a medium size mutt, likes to see if there is anything interesting in my garbage can. He likes to run in, check the garbage, and run out. He greets visitors to the floor with occasional barking. (Bella likes to bark, in general, if she's not getting enough attention from anyone.) Pre covid we would have an open studio day, in April, where we would allow/encourage visitors to bring their pets in. As the stairwell doors would be open you would hear occasional barking all day. It made for quite a social event, with dogs barking, and owners introducing themselves and their pets. It also made for good sales. Dog owners would take their dogs home and then come back later to purchase artworks.

From what you described, Sylvie, the decal colors have absorbed into the glaze. As they're now glass like I would suggest sand blasting. Find an auto shop/metal shop that does such things and ask if they would help you out. A friend of mine recently damaged her ceramic tub when she left a vinegar-soaked garment sit in the tub overnight. (It ate through the glossy surface.) You could try leaving vinegar on the offending areas for a day or two?

Hello Finnip, The answers, to Neil's questions, would help us have a better picture of what's going on with your situation. Without that I'll throw out a few broad suggestions: I wouldn't suggest adding anything to the plaster itself. If anything you could try other kinds of plaster. Ceramical, for RAM presses, is absorbent and quite durable. (More like cement than plaster.) It does absorb, just not as quickly, as pottery plaster. You would simply need to allow the slip to sit in the mold longer. The other factor, which Neil touches upon, is the consistency of your slip. If your slip has too much deflocculant that will cause early deterioration of your molds. Are you monitoring your deflocculation carefully? The last aspect is design of your model. Can you fill in the detail such that the mold is more durable but allow for easy touch up after the piece comes out of the mold? Sometimes its more cost effective to have a mold with less detail, but can cast more pieces, than a mold with fine detail, which wears out quickly.

Hey Kakes, The first thing to mention is your terminology. Typically stoneware clay is not considered "low-fire". It used to be considered "high-fire" (fired to cone 10) but more recently many bodies have been mixed to vitrify at a "mid-fire" temperature. (cone 6) Earthenware clay is more typically considered "low-fire". ( fired to cone 06) The two local companies, Minnesota Clay and Continental Clay, both sell earthenware clay but I know several potters who like to fire their earthenware pots to cone 2. In a sense any vitrified clay is highly durable. In my experience, however, earthenware tends to be a bit more brittle than stoneware or porcelain clay, after firing. As to which is best, that, I think, would be more about color range you want to work with. If you're finishing the pieces in glaze earthenware temps give you brighter colors and a broader color range. Hope this helps?

I have a thought to make quilted porcelain picture frames in gold. I'll high fire them to make them durable, cone 6, but am unsure about how to achieve a gold appearance. I don't think I want to work with gold lustres so that leaves me with gold paints? As those look unappealing, I'm thinking about gold leaf. Has anyone applied gold leaf to a ceramic surface and any tips on the process? Thanks

Back in the 90"s I was commissioned to make 200 porcelain figurines. I found a sculptor to sculpt the piece and then I made 10 production molds. After showing the customer a cast piece, unfired, they asked me if I could paint the piece. As I knew they couldn't finish the piece I agreed to include that in the project. (It was for a group home for people with severe disabilities.) Never having worked with "Amaco Underglazes" before I went out and bought about 20. Almost all of them were disappointing. (Except Medium Blue and Bright Yellow.) Frustrated I decided to "make my own". I bought a pint of the Amaco LUG white Underglaze and a bunch of Mason Stains. I experimented with mixing them, in various amounts, and found the homemade version to be quite good. There was a lot of frustration, but after awhile, I found a group of colors that safely went to cone 6 and were mostly opaque.

That's really amazing Jes! Another option would be to make a mold of the piece. Use alginate. Apply a small amount to a corner and see how it responds. My guess is that it releases easily. (Perhaps a light spray of water to moisten the surface?) After you've applied the alginate you would then back it with a plaster "mother" mold. A bit time consuming but an easy way to capture such fine work.

I purchased my first potters wheel, a Brent kick wheel, in high school. As we didn't quite know where to put it, in my childhood home, we put it in the back yard. It was wonderful to throw pots outside while making no noise and hearing the birds singing. But it was heavy, and awkward, so I sold it a few years later. I bought my first, and only, electric wheel in 1984. A Brent model C. I was convinced I would throw bigger pots and wanted a strong wheel. (The CXC was just coming into view.) It was a great wheel but it was heavy and not always quiet. (I'm told they've improved that since.) I turned to slip casting soon after and only occasionally used the wheel. (To craft round forms.) I developed a ruptured disc in 2006 and decided the heavy wheel had to go. Considering it was either more back pain, or no wheel, I was happy to see it go. I explain all of this to make apparent the fact that we never know how things will turn out. (The best laid plans...) I would suggest you go with Neil's advice and go with the Whisper. I know a young potter who has two and she loves them. She says they're fairly easy to move and she likes the quiet aspect..

Hey Alistair, While I know the 1.75 is considered the perfect SG have you had any luck with using more water than normal? In my own studio I work with a cone 6 porcelain and have no problem with the water level. (I don't measure in other words.) During the day, however, I work at a pottery that produces both cast and thrown stoneware pots. I did the SG weight test recently and found they like to run with a 1.68 SG level. (Meaning more water than normal.) Initially I thought that was a bit more water, than was necessary, but I realized the casters like it at that level so I let it be. Every clay is different and some adjust easily and some don't. A little experimentation can lead to unexpected results.

That sounds like fun Babs. Congrats! I would steer the women towards coil building mostly. That allows them to make a pot, of any size, of their choosing. Any time I tried to pinch a pot I was always limited to making small cup forms. (To make a tall pinch pot you really need to let the clay stiffen for a period of time. Is that something you can do in this limited situation?) If you choose to offer slabs of clay maybe you could bring coffee cans or plastic bowl forms that they can use to mold the slabs? Maybe cardboard tubes as well? When I was in my 20's I worked part time at a daycare center down the street from my studio. One day the head teacher, Dawn, asked me to introduce the kids to clay. For each of the kids, 15 in total, I made small slabs of clay and a few coils. Seven of the children decided to make nests with their slab and coils. What was really cute was that each off the kids had a little story to tell about their nest. (Each had also made little ball forms which represented the eggs.) The whole experience went in a direction I did not expect and was rewarding as a result. I hope you have similar success.

I think Roberta has the better suggestion. The depth of the fabric makes it very challenging to plaster. Rather than have that challenge just roll the fabric into a soft clay slab first and see if you like that.

Hello Vika, It would appear that this is fabric, correct? In that case you need to seal the material before casting. A spray urethane would be best for that. You would probably need to apply several coats. Apply the urethane thick enough so you see a glossy reflection. That will tell you the fabric is sealed. Murphy's oil soap only works on porous materials like plaster or wood. As there appears to be many undercuts you may run into problems with the plaster getting stuck in the crevices. A simple way to seal those holes would be to apply a thin coat of plaster and then wipe the fabric with a sponge BEFORE the plaster sets up. Allow that layer to dry (30 minutes) Then apply a thin coat of Murphy's to the surface. This will be a difficult thing to mold. Be prepared for a few challenges.

If we can take the firing issue off the table we're left with process. Two thoughts: 1) how much grog have you used? You may have too much in the clay, and 2) water- do you throw with lots of water? Perhaps the clay is getting too wet, in the throwing process, and its causing this shrinkage/cracking? The other thought: to pick un on the Pres point, are you spending a lot of time trimming the pot? Making three rings must take awhile? Perhaps too much contact with the trimming tool. Have you tried not trimming the pots with a tool? (Leave them unfooted in other words.) Maybe use a trimming stick on the wheel and leave it at that.