A workshop in Banská Štiavnica

A mix of lime, sand and, where needed, gypsum, modelled into the relief decoration of ceilings, vaults and facades. Unlike a cast, true stucco is run or modelled in place — every piece is therefore unique, and in restoration it cannot simply be replaced with a stock part.

A cornice is not cast but run: a sheet-metal template with the profile cut into it is drawn repeatedly along a guide rail, smoothing the exact shape out of fresh mortar. The tool is a plain piece of tin — but the profile differs from house to house, so restoration begins by measuring it off whatever survives.

A lighter coat of render is laid over a darker ground and, while it is still damp, the drawing is scratched through to the layer beneath. The technique came out of the Renaissance and survives in places on the facades of Banská Štiavnica. It can only be repaired by repeating the whole process, never by painting over it.

Bole is laid under the gold leaf — a fine red clay that gives the gold its depth and lets it be burnished to a high shine with an agate. That is why red always shows through worn gilding; it is the mark of true leaf gold, not a fault.

Gypsum is coloured and built up in layers so that, once ground down and polished, it looks like cut stone — the technique is also called stucco lustro. It is used where real marble would be too heavy or absurdly expensive, and the surest way to tell it from stone is that it feels warm to the touch.

Ageing a surface on purpose: glazes, darker deposits in the hollows, and polished highlights where years of handling would have worn it smooth. In restoration it settles a new piece against the original; in the film workshop it turns a freshly cast object into a hundred-year-old one.

Painting that pretends to be architecture or material which is not really there — a cornice, a column, an open sky. It only ever works from one particular spot in the room, which is why it is not drawn in a studio but designed on site.

A faithful scale version of something that cannot be carried into a display case — a cave, a mine working, a karst spring. It has to be right to a specialist, not merely convincing to the eye, so it is made together with the people who study the thing itself.