There is a point where casting stops being an experiment and starts being a practice. It usually arrives when someone asks whether they can buy the thing you made.
What follows is mostly about repeatability — the difference between having made a good object and being able to make it again.
Designing for the mould
Once you design your own forms, the mould stops being a container and becomes part of the design problem.
- Avoid undercuts
- A shape wider inside than at its opening will not release, no matter how flexible the silicone. If a form has to have one, it needs a mould that comes apart.
- Give the walls a slight taper
- Sides that open outwards even slightly release far more easily than perfectly vertical ones. This costs nothing at the design stage and saves broken pieces later.
- Keep wall thickness even
- Abrupt changes from thick to thin dry at different rates and concentrate stress where they meet. Even sections behave predictably.
- Ease sharp internal corners
- A softened internal corner fills better, traps less air and is much less likely to become the place a piece cracks.
Making the same object twice
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Write the recipe down
Ratio, total mix weight, pigment and quantity, mixing time, how long before demoulding, how long before sanding, which grits. Seven lines.
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Change one thing at a time
If you change the ratio and the pigment together and the result improves, you have learned nothing you can use.
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Cast in sets, not singles
Three pieces from one mix tell you how consistent your process is. One piece tells you only about itself.
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Keep a reference piece
Put one good example aside and never sell it. It becomes the standard everything else is judged against.
Working in small batches
Batch work changes the bottleneck. It is rarely the pouring — it is the drying space, the sanding time and the moulds you have available.
Two moulds of the same form will roughly double your output for a fraction of the effort of speeding anything else up. Most people buy more material when what they needed was another mould.
Plan the run backwards from the finishing stage. Twelve pieces demoulded on the same evening means twelve pieces to sand, and that is the day that actually costs you.
If you start selling
- Cost the whole object
- Material, pigment, the share of the mould, packaging, and your hours at the sanding table. Most first prices cover the powder and nothing else.
- Consistency is the product
- A buyer of a set expects the set to match. This is where written notes stop being tidy and start being commercial.
- Describe honestly
- Until our testing is published, describe pieces as decorative and indoor, and do not repeat performance claims you have not verified yourself. Your reputation is attached to what you say about the object.
- Photograph in daylight
- Soft, natural light on a warm neutral surface shows a mineral material accurately. Hard artificial light flattens exactly the surface quality you worked for.
