Terra Cotta slip powder was our second ceramic powder tested in our lab. It has OK damp strength, good green strength, and has interesting behavior in the kiln cycle.

SPS Redart Terracotta Slip – 1000 units

Powdered Sugar   ———– 250 units

Maltodextrin   ————- 250 units

If you can’t find Maltodextrin, then use Benefiber (it is no longer maltodextrin but rather a wheat dextrin).

We are like the nature of Terra Cotta as it changes color and strength depending on how high you fire it.

Terra Cotta Test fires

Terra Cotta test firings.  Notice that there is more shrinkage and the color gets darker as temperature goes up.

18 Comments on RedArt Terracotta Slip

  1. Carlo Sammarco says:

    Hi guys,

    I’m wondering how you mix all your dry powders. We’ve always been taught that wet mixing is the way to go (in ceramics), but assuming we are using water, won’t the sugar react with the Maltodextrin (or Benefiber) in a non-reversible way? Should we consider a dry-mixing technique instead? I’m not sure if this is already covered elsewhere on your site…

    On a side note… this site rocks!!!

    TIA,

    Carlo

    • admin says:

      Carlo, I hope that you are not disappointed but we use a small cement/mortar mixer from Harbor Freight.

      http://www.harborfreightusa.co.....emid=91907

      The small model almost fits a 5 plastic gallon pail. Our shop master (Kevin) cut slits in the top of the mixer to make it act as a spring-chuck to nicely hold the plastic 5 gallon pail. We found a piece of old pulled steel grating that we cut and bent into a “V” to fit inside the bucket to aid mixing. Weight out the ingrediants, add the pulled steel mixing aid, place pail into cement mixer, and then start. Mix for 20-30 minutes. What’s even better about this rig, a 2 gallon pail just fits inside a 5 gallon pail for small batch mixing. Cheers!

  2. Carlo Sammarco says:

    Hi guys,

    I’m wondering how you mix all your dry powders. We’ve always been taught that wet mixing is the way to go (in ceramics), but assuming we are using water, won’t the sugar react with the Maltodextrin (or Benefiber) in a non-reversible way? Should we consider a dry-mixing technique instead? I’m not sure if this is already covered elsewhere on your site…

    On a side note… this site rocks!!!

    TIA,

    Carlo

    • admin says:

      Carlo, I hope that you are not disappointed but we use a small cement/mortar mixer from Harbor Freight.

      http://www.harborfreightusa.co.....emid=91907

      The small model almost fits a 5 plastic gallon pail. Our shop master (Kevin) cut slits in the top of the mixer to make it act as a spring-chuck to nicely hold the plastic 5 gallon pail. We found a piece of old pulled steel grating that we cut and bent into a “V” to fit inside the bucket to aid mixing. Weight out the ingrediants, add the pulled steel mixing aid, place pail into cement mixer, and then start. Mix for 20-30 minutes. What’s even better about this rig, a 2 gallon pail just fits inside a 5 gallon pail for small batch mixing. Cheers!

  3. Carlo Sammarco says:

    Disappointed? Not at all!

    Sometimes I tend to over analyze/engineer/think things. Your reply is a relief. Even in ceramics, wet mixing isn’t always ideal. In some cases, not having particles intimately mixed actually allows for degassing during firing which reduces defects.

    I often dry-mix large batches of glaze recipes using a 5 gallon bucket with home-made vertical fins inside (like a clothes dryer). The bucket rotates on a ball mill unit. This sounds almost exactly like what you are doing. I also just noticed a small V-Mixer in one of the labs. It looks like it hasn’t been used in a while and may be just right for this project.

    I’ll let you know how it goes…

    Thanks!

    Carlo

  4. Carlo Sammarco says:

    Disappointed? Not at all!

    Sometimes I tend to over analyze/engineer/think things. Your reply is a relief. Even in ceramics, wet mixing isn’t always ideal. In some cases, not having particles intimately mixed actually allows for degassing during firing which reduces defects.

    I often dry-mix large batches of glaze recipes using a 5 gallon bucket with home-made vertical fins inside (like a clothes dryer). The bucket rotates on a ball mill unit. This sounds almost exactly like what you are doing. I also just noticed a small V-Mixer in one of the labs. It looks like it hasn’t been used in a while and may be just right for this project.

    I’ll let you know how it goes…

    Thanks!

    Carlo

  5. Carlo Sammarco says:

    Hey guys/gals?,

    I finally started printing some ceramics today! Still drying in the machine as I type.

    I ended up mixing a recipe from scratch, drying it out, and then feeding it through a plate mill. I looked at the commercial plaster powders we have been using to get a sense of size. They pass through a 40 mesh screen with only a small residue on the screen so 40 mesh is what I used for screening the crushed clay. The maltodextrin also passed through to 40 mesh with just a bit of residue.

    I am using a 310 series machine and read your warning about the cartridge not liking to be purged. So for now, I’ve left the commercial binder in the machine and am using it instead as my binder.

    One thing I noticed while printing:

    On the feed chamber side: the clay mixture spreads quite differently than the commercial plaster powder. Whereas the plaster seemed to flow nicely on the front side of the roller, the clay doesn’t. It seems to want to agglomerate under the spinning roller. Every so often (perhaps 10 passes) the pressure builds up and eventually it goes all at once, resulting in slight tearing on the surface.

    On the build chamber side: The powder never really gets perfectly smooth like it would with the commercial plaster. There are always areas that remain “pitted”. These pitted areas never get filled as the powder isn’t really loose and able to do its own thing (as mentioned above).

    I’m wondering if you’ve had the same problem and if so, how you fixed it. I’ve tried both really compressing the powder in the build chamber, and hardly compressing it at all prior to starting. The latter seems to work better but still not as well as it think it should.

    As a follow-up question, how is the SPS clay being sold? As a powder? If so, can you tell if it has been spray dried (is it in the form of very small spheres, or does it just look like a normal powder? I know morphology of particles can play a huge role in how they spread.

    Thanks,

    Carlo

    • ganter says:

      Carlo, congrats on taking a first big step and thanks for sharing your results. As a community, we are stronger by having more people experiment. Replacing your powder with clay is a great way to start.

      We purchase all of our ceramics in dry mix form (then we add powdered sugar and maltodextrin and mix). SPS and Laguna Clay sell “dry slip” body (although I’ve been informed that dry slip is an oxymoron). These powders are screened somewhere between 400-600 mesh screens (about 10x smaller than what you are using). The target is around 40 microns. (25.4mm per inch /600 wires per inch = 42.3 microns). Although, we have been printing in glass using particles as large as 200 microns (think 120 mesh screen). The larger particle size really limits what details are possible.

      Many of the powder spreading details that you’ve seen are likely an issue of particle size (OR you have major moisture issues). You are running at about 600 microns particles from the 40 mesh screen. If your spreading a layer at 0.004 in (or 101 microns), it is really tough to get your particles to spread as your particles are about 5x taller than your spreading height.

      A quick test would be to spread a thicker layer and see if you have better results. You will need to adjust your powder settings in software. To get to 0.007 or 0.008 in layers, you will need to change material type to a non-plaster material.

      Please keep us posted.

  6. Carlo Sammarco says:

    Hey guys/gals?,

    I finally started printing some ceramics today! Still drying in the machine as I type.

    I ended up mixing a recipe from scratch, drying it out, and then feeding it through a plate mill. I looked at the commercial plaster powders we have been using to get a sense of size. They pass through a 40 mesh screen with only a small residue on the screen so 40 mesh is what I used for screening the crushed clay. The maltodextrin also passed through to 40 mesh with just a bit of residue.

    I am using a 310 series machine and read your warning about the cartridge not liking to be purged. So for now, I’ve left the commercial binder in the machine and am using it instead as my binder.

    One thing I noticed while printing:

    On the feed chamber side: the clay mixture spreads quite differently than the commercial plaster powder. Whereas the plaster seemed to flow nicely on the front side of the roller, the clay doesn’t. It seems to want to agglomerate under the spinning roller. Every so often (perhaps 10 passes) the pressure builds up and eventually it goes all at once, resulting in slight tearing on the surface.

    On the build chamber side: The powder never really gets perfectly smooth like it would with the commercial plaster. There are always areas that remain “pitted”. These pitted areas never get filled as the powder isn’t really loose and able to do its own thing (as mentioned above).

    I’m wondering if you’ve had the same problem and if so, how you fixed it. I’ve tried both really compressing the powder in the build chamber, and hardly compressing it at all prior to starting. The latter seems to work better but still not as well as it think it should.

    As a follow-up question, how is the SPS clay being sold? As a powder? If so, can you tell if it has been spray dried (is it in the form of very small spheres, or does it just look like a normal powder? I know morphology of particles can play a huge role in how they spread.

    Thanks,

    Carlo

    • ganter says:

      Carlo, congrats on taking a first big step and thanks for sharing your results. As a community, we are stronger by having more people experiment. Replacing your powder with clay is a great way to start.

      We purchase all of our ceramics in dry mix form (then we add powdered sugar and maltodextrin and mix). SPS and Laguna Clay sell “dry slip” body (although I’ve been informed that dry slip is an oxymoron). These powders are screened somewhere between 400-600 mesh screens (about 10x smaller than what you are using). The target is around 40 microns. (25.4mm per inch /600 wires per inch = 42.3 microns). Although, we have been printing in glass using particles as large as 200 microns (think 120 mesh screen). The larger particle size really limits what details are possible.

      Many of the powder spreading details that you’ve seen are likely an issue of particle size (OR you have major moisture issues). You are running at about 600 microns particles from the 40 mesh screen. If your spreading a layer at 0.004 in (or 101 microns), it is really tough to get your particles to spread as your particles are about 5x taller than your spreading height.

      A quick test would be to spread a thicker layer and see if you have better results. You will need to adjust your powder settings in software. To get to 0.007 or 0.008 in layers, you will need to change material type to a non-plaster material.

      Please keep us posted.

  7. Carlo Sammarco says:

    Very cool Mark,

    This is exactly the kind of info I can understand and use. Thanks!

    I was actually thinking it might be a moisture issue (it’s been very humid here the past week). To prove/disprove this, I might try spreading non- hygroscopic material… perhaps powdered flint or feldspar.

    One last question if you don’t mind. I understand the issue of mesh sizes. So the clay you are using is between 400-600 mesh. I won’t have a problem preparing this. I assume the powdered sugar is similarly fine. But what about the Maltodextrin? The Maltodextrin I have is from Tate and Lyle (Star-Dri 100). It resembles granulated sugar in size and some doesn’t pass the 40 mesh (let alone a 400 mesh). Should I try grinding it so it passes the 400-600 mesh range? Should I source finer material? Or should I not worry about it?

    BTW, I am going to start up a blog so I don’t ramble on your site!

    Thanks,

    Carlo

    • ganter says:

      Carlo, the Tate & Lyle malto is fine. If the majority of your powder is fine, you can tolerate a few big particles (it all about particle distribution).

      If it is humid, Malto is a strong hygroscopic material. Humidity is a real issue.

      As soon as your blog is up, please let us know, so we can add you to our blog roll.

  8. Carlo Sammarco says:

    Very cool Mark,

    This is exactly the kind of info I can understand and use. Thanks!

    I was actually thinking it might be a moisture issue (it’s been very humid here the past week). To prove/disprove this, I might try spreading non- hygroscopic material… perhaps powdered flint or feldspar.

    One last question if you don’t mind. I understand the issue of mesh sizes. So the clay you are using is between 400-600 mesh. I won’t have a problem preparing this. I assume the powdered sugar is similarly fine. But what about the Maltodextrin? The Maltodextrin I have is from Tate and Lyle (Star-Dri 100). It resembles granulated sugar in size and some doesn’t pass the 40 mesh (let alone a 400 mesh). Should I try grinding it so it passes the 400-600 mesh range? Should I source finer material? Or should I not worry about it?

    BTW, I am going to start up a blog so I don’t ramble on your site!

    Thanks,

    Carlo

    • ganter says:

      Carlo, the Tate & Lyle malto is fine. If the majority of your powder is fine, you can tolerate a few big particles (it all about particle distribution).

      If it is humid, Malto is a strong hygroscopic material. Humidity is a real issue.

      As soon as your blog is up, please let us know, so we can add you to our blog roll.

  9. Ira Abeleda says:

    good job with the clay Carlo! tried it also and it worked somehow. thanks for sharing your experiment results here. glad to have read the comment thread 😉

  10. Ira Abeleda says:

    good job with the clay Carlo! tried it also and it worked somehow. thanks for sharing your experiment results here. glad to have read the comment thread 😉

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