Sandcastle Rule: If this structure was made of wet sand, would it break?
There's a part in the production process for ceramics 3D printing during which the model is fragile and brittle. It's basically like wet sand. When you design, ask yourself this question: if I made this out of wet sand or brittle clay, could I lift the design without it breaking? If the answer is "no," then your design might break in production.

Your model should have a strong and obvious base
These pieces need to be glazed. While they're being glazed (meaning it is toasting in the oven), they needs a base to support it. Pieces with a clear base will be much more likely to glaze well than pieces without a clear base. For pieces without a clear base, we have support structures, but the support structures might leave small dents or craters in the surface of the glaze.

Hard to reach places might not have glaze applied
Please be aware, places that are not glazed are not foodsafe. If you design a crazy straw that has all sorts of twist and turns, the inside of the straw might not have glaze. Most cups, bowls, and plates should have no problem being glazed in places that come in contact with food. Note, the bottom of cups / bowls / plates will not be glazed.

Glazing adds thickness
Glazing will reduce definition of design details, such as grooves will fill with glaze. Up to 1mm of glaze can be added in certain areas. Take a look at this render and the actual product. See how the glaze found its way into the grooves between the beads?

Multiple parts per STL
When putting multiple parts in one STL file (i.e., a cup and a lid), please keep in mind the following. First, parts should be separated and not nested. Second, parts should all be oriented so that the height of the parts are roughly the same. Individual parts should have bounding box dimensions adding up to 120mm.

Curve your edges
Joining faces should have a radius of 2mm. A good question to ask is: Can you snugly fit a ball bearing with a 4mm diameter into the corner of your piece? If there's a gap between the corner and the ball bearing, then it is too sharp. Sharp corners are likely to crack when heated.

Strut your stuff
Thin struts cannot be attached to large unsupported sections. Unsupported struts should be less than 8 mm in length.

Fat Bottom Designs
Large sections should be lower in the model to add stability. If you have a structure like this picture, please add a base to stabilize the print.

Holes for Hollow Parts
Holes in pieces must be at least 5mm in diameter. If you only have one escape hole for your hollow part, that hole must be 10mm in diameter. This is to help with the depowdering process, as well as ensuring the glaze does not seal the hole.

Decorative Holes
For decorative holes, please keep the holes above 5mm in diameter. This also applies for things like necklace loops.

Smooth Edges
Edges should be smooth. Knife edges (or tapered edges) and serrated edges will crack in the production process.

Designing for pieces that fit
Pieces that "fit" together are tough, but if you have to design this please keep a clearance of 4mm. For pieces that fit (ie teapot lid and teapot), the clearance between the designs should be 4mm. This is because the glaze will add up to 1mm of surface volume in some places. We do not guarantee tight fits but if you follow this rule, you should at least get a loose fitting part.