|Monthly Tech-Tip |
This is made from 100% of a natural clay (3B) from the Whitemud formation in Ravenscrag, Saskatchewan. To make this body, which I call MNP, I slake and slurry up the raw clay lumps, sieve it to 200 mesh and then dewater on a plaster table. I rolled the plastic clay into a thin layer, cut it into a cross-shape using a 3D printed cookie-cutter, drape-molded it over a plaster form and then slip-joined the seams. It fires very dense and strong (to zero porosity like glass!). It holds together well and joins well with its own slip. Although not super plastic, it is smooth and fine-grained like a commercial porcelain body. I add 1-2% bentonite to make it more plastic when needed. It has the ability to be rolled extremely thin and yet does not warp in the firing! This mug has a weight-to-volume ratio of 2.08 (the weight of water it will hold compared to its own weight).
You may already know that I am very excited about the potential of 3D printing for creating aids to making pottery. I glue four of these together to create a cookie cutter for producing my slab-built mugs. For different sizes of mugs I need cutters with different geometries. This is quarter-cutter and it has been drawn "parametrically" using Fusion 360. That means that certain aspects of its geometry (two lengths and one angle) can be changed by simply changing the parameters (in the Parameters dialog). The drawing then adjusts automatically. It is magic! Other aspects are fixed (e.g. the right-angle, the pucker-preventing hole cutouts, the height, thickness). Parametric design is revolutionary, it fits my try-it-adjust-it-try-it-again way of working. And, I can label these printed quarters according to the parameters, in this case 45-25-108.
These four sections were glued together to make a larger one. Now it is possible to quickly precision-cut the shape for making my pie-crust mugs. Later I re-printed these templates on a better 3D printer so the inner vertex holes cut out much better.
This cookie cutter can both cut and stamp the piece (notice the 3D render in the centre, the logo is 2mm lower than that cutter around the outside). We make them by rolling a slab to 3.2mm (1/8in) thick, applying stretch wrap over it and then pressing the cutter/stamper into it (using a wood block). Then just peel away the plastic and the outer waste clay and a perfect crest is left. This method enables using clay of almost any stiffness. We find that softer clay works best, just peel it up from the board, apply slip to the back, position it on the side of the leather hard ware and press it down (from the centre outwards). On the lower right is a crested mug that has just been glazed. Upper right is a crest that has been glazed and fired. About the cookie cutter: We create them with 0.8mm wall thickness (twice the width of the 0.4mm extruder on the 3D printer). We export the vector image (made in Illustrator) into Fusion 360 and then add elements to stabilize and hold the profile in place. This cutter is 8mm tall and the stamp lines are 5mm tall. The crest is 52mm (2 in) wide. This whole process may sound a little intimidating to you - but we are working on a step-by-step video.
Blender mixing is invaluable in slurry preparation in small scale ceramics and testing. It is quick and so effective that not only are particle surfaces wetted much better but clay particles can actually be reduced in size (literally ground finer). Slurry rheology is also stabilized. For example, thixotropy can often be achieved naturally, without any additives. Materials that are otherwise impossible to mix into a slurry (e.g. bentonite, Veegum, CMC gum) are no problem. Even slurry-processed porcelains benefit, not only being more plastic, but firing to a more homogeneous surface and to greater density. Just visually, it is easy to see how much improved this MNP slurry is (a local clay with porcelaneous properties). It was mixed using our propeller mixer and seemed OK (on the left). But the improvement after only 20 seconds in the blender (right) is amazing.
Of all the pieces I make, ones like these mean the most to me. To make this cup I sieved a Plainsman 3D clay slurry to 325 mesh to produce a natural porcelain that vitrifies beyond the zero porosity point at cone 6, yielding incredibly strong ware. I make the outside and inside glazes from clays we mine in Montana and Alberta (using chemistry to maximize the clay percentage to more than 70%).
Mother Nature's Porcelain - Plainsman 3B
Pie-Crust Mug-Making Method
Tony Hansen's project to make light, strong and functional slab-built mugs using tools and templates made possible by 3D design and 3D printing.
How to Find and Test Your Own Native Clays
Some of the key tests needed to really understand what a clay is and what it can be used for can be done with inexpensive equipment and simple procedures. These practical tests can give you a better picture than a data sheet full of numbers.