Broadening Horizons

 Posted by at 5:55 pm  Ceramics
Aug 212012

In the spirit of consolidating my online identity onto a server I control and actually own the content, I’m repurposing to include non-software stuff I’m into as well as the software and technology related stuff I’ve posted here for years. I have been intending to build separate sites for my various fields of interest, but why fragment? Put it all in one place and index accordingly.

First stop: Ceramics.

I was a good little potter and made a photo catalog of (almost) all of the pieces I made in the two week run up to the Bonny Doon Studio Tour this past July. Good thing, too – I sold nearly 20 pieces that weekend! I’m now starting to post those photos and notes here under a new “Ceramics” section.

I do slip cast stoneware. That means making/using a plaster mold, pouring liquid clay into the mold, waiting for a clay skin to develop on the mold surface, and pouring off the remaining liquid. Dry, demold, dry some more, clean up parting lines, dry still more, bisque fire, glaze, dry, and glaze fire. Each piece takes about 10 days to complete, including two 24 hour kiln firings.

I use old plaster molds found in garage sales, freecycle, and curbside. I make my own traditional poured plaster molds from found objects.

I also design 3D models in software and make plaster molds from the models using a ZCorp model 406 3D powder printer I bought at auction about 2 years ago. Though 3D printing has only recently become a popular Internet meme, 3D printing technology actually dates back to the early 90’s at MIT. My Z406 machine was built in 2004, long before I was even aware of 3D printing.

It took me more than a year of nights and weekends to get that beast up and running again after sitting unused for years in some warehouse. I replaced clogged fluid lines, learned the special little ritual to get it to take a new print head without burning it out in the first 30 seconds, and many more colorful stories of man-machine bonding. And swearing. And vodka. Lots of vodka. For the machine, of course. No, seriously – HP Thermal inkjet printheads don’t work well with pure water. They prefer a 24% alcohol solution with a 4% glycerin chaser.

My ultimate goal for the powder printer is to print directly in clay powder and fire the printed piece in the kiln to achieve working strength, and then continue with traditional glazing and decoration techniques from that point on. Recipes published by the U of Washington Open3DP blog have been a great start, but I’m continuing to refine and experiment with powder recipes to suit my objectives and to suit my finicky machine.

Until I get clay powder printing sorted out to my liking, printing in plaster is a viable alternative. I can print open face one-part molds in plaster using off the shelf materials (Hydroperm plaster) and use them exactly as I would a traditional slipcast plaster mold.

The main differences between printed plaster molds and traditional plaster molds are:

  1. Poor surface quality of the printed molds. Traditional poured plaster forms a silky smooth extremely tight pore structure that printed plaster just can’t match.
  2. Printed molds are not as durable as traditional plaster molds. A traditionally made poured plaster mold will last for hundreds of castings with proper care. A printed plaster mold will only last for a few dozen castings before the working surface deteriorates beyond use.
  3. Printed molds have a larger pore structure than traditional plaster, which means the capillary forces that draw water out of the slip and leave clay behind on the mold surface are weaker in a printed mold. This isn’t a major issue, it just means casting takes longer (20 to 90 minutes) with printed molds than with traditional molds (10-30 minutes).
  4. It is possible to print multipart molds for complex shapes with all the registration marks needed to get everything to line up correctly, but this requires a lot of extra setup work in the 3D modelling software and factoring in swelling, shrinkage and bleed make it very tricky to get matching mold parts that fit together perfectly.

About a third of the ceramic pieces I made for the July show were made using “factory” made molds, a third with traditional poured plaster molds I made myself, and a third of the pieces were made with a 3d printed plaster mold, now known by the unremarkable name “3D plaster mold #1.”

Here are a few of examples of bowls created from that first 3D printed mold:

Green Rimmed Red Bowl

Black & Tan


The bowl is a bit small – a little over 5 inches in diameter with a flared flat rim and the cutest little foot on the bottom. The Z406 printer’s build area is 8 inches wide, and the mold needs about an inch of plaster thickness on all sides to provide enough capillary force for slipcasting, so after plaster shrinkage in drying and clay shrinkage in firing the largest piece I can cast from a one-piece printed mold is a little over 5 inches wide.

I’ll be printing a set of new molds in the near future and will post details of the process and the results.