A demoulded piece is not a finished piece. The difference between the two is usually twenty minutes of patient work on the edges.
Most of the visual quality of a cast object lives in two places: the rim, and the face you look at most.
Working the surface
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Start with the edges
The rim where the material met the top of the mould is almost always the roughest part. Take it back first — it is the part a hand finds and the eye reads as quality.
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Work through the grits in order
Begin coarse enough to remove what you want gone, then step through progressively finer grades. Skipping grades leaves scratches from the coarse paper that the fine paper cannot reach.
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Sand flat things flat
Wrap the paper around a flat block for flat faces. Fingers follow a surface’s existing bumps and preserve them.
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Check in raking light
Hold the piece so light travels across the surface rather than straight at it. Every scratch and low spot appears immediately.
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Clean off the dust
Dust hides exactly the flaws you are trying to find, and it sits in the surface if you seal over it.
What sealing does
Sealing is a surface treatment applied after the piece is finished and dry. Broadly, it does two things: it changes how the surface looks — depth, sheen, how saturated the colour reads — and it adds a layer between the object and the world.
It is worth deciding what you want from it before you buy anything. A sealer chosen for appearance and a sealer chosen for protection are not always the same product.
Things worth knowing
- Sand dry pieces, not fresh ones
- A piece that still holds moisture clogs paper and finishes unevenly. Give it time before you start.
- Wear a dust mask
- Sanding any mineral material produces fine dust. Work in a ventilated space and follow the safety guidance supplied with your bag.
- Colour looks different once sealed
- Most surface treatments deepen colour. Test on an offcut or an early piece before you seal something you care about.
