Digital manufacturing techniques in pottery

Software used

Engineering design software such as SolidWorks and Fusion 360, used to design pieces to precise dimensions and to design moulds and stamps from the same file.

Freeform modelling software such as Rhino and Blender, suited to organic and sculpted forms that are hard to draw from dimensions alone.

Parametric design tools such as Grasshopper and the WASP parametric design app, in which the designer controls form, size and texture through variables; the app exports a G-code file ready to print directly.

Slicing software such as Cura and Simplify3D, which converts the model into layers and a toolpath the printer understands, while CNC toolpaths are prepared in software such as VCarve.

Design considerations

Shrinkage: Clay shrinks during drying and firing, so the design is scaled up in advance. If shrinkage is 15% and the required finished diameter is 100 mm, the diameter in the design is about 117.6 mm. It is best to measure the actual shrinkage of the clay being used with test samples.

Wall thickness: This is set to suit the forming method: in clay printing it depends on the nozzle diameter, and in slip casting on how long the slip stays in the mould.

Mould design: Slight draft angles are added to help the piece release, the parting line between the mould parts is defined, and undercuts that would prevent the piece being removed are avoided.

Clay printing: Overhangs need attention, because steeply angled parts without support can collapse before the layers firm up.

From file to machine

Models for printing are exported in formats such as STL and OBJ, then sliced into G-code. Models for moulds are exported in formats such as STEP to prepare the carving toolpaths, and flat designs for stamps and decoration are sent to the laser in vector formats such as DXF and SVG.

How are they made?

The stamp is designed on the computer with the required pattern, then printed in a plastic such as PLA. Flat stamps can be printed for logos and small patterns, or rollers that are run over the clay to add a repeating pattern across a larger area.

The stamp is pressed into the clay while it is soft but firm, before it dries, leaving a clear incised impression without distorting the piece.

Helper tools

The same printer is used to print tools that make the work easier, such as locks that hold mould parts together and pouring spouts that act as a reservoir for the slip.

How are they made?

The laser engraves the design into the acrylic sheet deep enough to impress clearly in the clay, then cuts the stamp to its final outline on the same machine. Engraving is done before cutting so the piece does not shift between the two operations and throw the detail out of alignment.

The design is mirrored horizontally before engraving, so that lettering reads correctly once pressed into the clay. Engraving in several passes at lower power is preferable, for cleaner edges and crisper relief.

Printing and transfer

Designs are printed on decal paper with a dedicated laser printer that uses ceramic toner. The print is covered with a thin clear layer that carries the image and burns away during firing, either because the paper comes pre-coated or because the layer is applied after printing.

The decal is then soaked in water for a few seconds until it slides off the paper, placed on the piece and smoothed down to push out any air bubbles and water from underneath.

Fixing by firing

The decal is applied to the piece after it has been glazed and fired, and the piece then goes through an additional firing whose temperature depends on the type of toner and the result required:

On-glaze: At a lower temperature, approximately 700–840 °C, so the colour fuses to the surface of the glaze.

In-glaze: At higher temperatures, approximately 920–1,250 °C, so the glaze softens and the colour sinks into it, as with tiles and sanitaryware.

On glass: With a dedicated toner fired at the lower temperatures suited to glass.

Exact temperatures vary with the type of toner and glaze, and are taken from the supplier's technical data sheet.

How does it work?

A CO2 laser engraves directly onto the surface of the glazed piece after firing, removing a thin layer of glaze where the design falls. The engraving shows as a matt texture that contrasts with the glossy surface around it.

What to consider

Because ceramics are hard and brittle, power, speed and focus are set after a trial on a test piece to avoid cracking or breakage, and the piece is held firmly on the work surface. The machine is used with adequate ventilation, as engraving produces fine dust.

The firing programme

A firing programme consists of successive segments, each with a heating rate, a target temperature and a hold time. Programmes usually begin with slow heating that drives off residual moisture without damaging the pieces; the temperature is then raised to its peak and held for a set time, and the kiln is cooled at a controlled rate.

Ceramics usually go through two firings: a bisque firing that turns the clay into a hard piece ready for glazing, then a second firing after glazing. A third firing may be added for decals applied on-glaze.