Excerpt from CM Article:
http://ceramicartsdaily.org/methods-techniques/the-printed-pot/
“In Sachs’ lab at MIT, ceramics (i.e. alumina) were among the original materials explored for use in 3DP. Currently, however, 3DP suppliers do not provide art-ceramic powder as an option which presented a large barrier to the use of 3DP by ceramic artists, so we decided to knock down that barrier. To do so, we would need to select a ceramic powder, decide on appropriate additives, and design the appropriate printing fluid; but what powder should we try first?
We recently had some students experimenting with casting metal into a low fire (Cone 06) slip locally known as Xtra-White. Since we had this slip on hand in powder form, it seemed like the obvious initial choice. We loaded up the 3D printer with Xtra-White slip powder, and used an existing alcohol-water solution as binder. It seemed like a good first test as simply mixing slip with water and letting it dry produces a functional greenware. Let’s just say our first 3D printing tests were not terribly successful. The parts were so weak that any contact caused crumbling, and we could not remove the parts from the powder bed. However, the slip powder spread extremely well and had a very nice surface finish on the printing-bed surface.
We needed to find a water-soluble “glue” to add to the slip powder to give strength to the printed parts. (The “glue” could also be added to the printing fluid, but keeping the glue in the powder bed avoids problems with clogged print heads.) The parts needed to be strong enough to survive general human handing, depowdering, and kiln firing. Again, the numbers of choices we have for in-powder-bed “glues” is quite large with PVA (PolyVinyl Alcohol), PVAc (PolyVinyl Acetate), SCMC (Sodium CarboxyMethyl Cellulose), PolyOx (Polyethylene Oxide), and various carbohydrates being high on the list of choices. Previously, we had run hundreds of test powder mixtures along with various water/alcohol binder setups. (The process is not too different than glaze or clay formulation experiments – choose a test shape that is significant and keep good notes.) Based on experience, experimentation, and a strong desire to produce a low-cost powder, we settled on a combination of PVA (PolyVinyl Alcohol), and extra-fine sugar as additives with the Xtra-White slip powder along with an alcohol-water binder. After many more test runs (each one with different printing parameters), we finally succeeded in printing parts that could be removed from the 3D printer bed and depowdered. We focused on test bars which were 10x10x100 mm as they printed quickly and didn’t require large quantities of powder to be mixed. Now, it was time to test fire the bars (in lots of five). Since, the Xtra-White was a Cone 06 slip, it seemed that a Cone 06 firing (1828 oF/997 oC) was in order. When the test bars were examined after the firing, they crumbled to the touch and exhibited minimal strength. We continued firing more test bars (and gathering additional data) at increasing temperatures until the test bars “melted to the kiln shelf”. Having determined proper parameters for printing and firing, we were able to move on to fabricating simple functional shapes (small votive candle holders, see Xtra post).
Encouraged by successfully printing with Xtra-White, we moved on to a higher firing slip, Redart TerraCotta. With the same powder additives and overall 3DP setup, we started printing TerraCotta, and it worked immediately! We followed a similar testing process, firing bars in sets of five at progressively higher temperatures until the TerraCotta “melted to the kiln shelf”. Again, we moved from printing bars to printing more interesting shapes (see TerraCotta post).”