Darwi is a self-hardening modeling clay made by The Clay and Paint Factory in Liège, Belgium — the same factory, and the same people, behind Cernit. There is no oven and no kiln: you shape it and leave it, and it hardens in open air.

Darwi describe it as a 98% natural product, and it is non-toxic, odorless, gluten-free and vegan — worth knowing if you are handing it to a classroom or a workshop. It is supple and semi-elastic, it does not stick to your hands, and you can work it with bare hands rather than gloves. The grain is fine enough to hold real detail.

It grips other materials. Darwi bonds to wood, polystyrene, ceramic, glass and plastic, which is what makes it useful beyond modeling from scratch — building onto an existing object, bulking out a form over a cheap polystyrene core, or repairing a broken piece of furniture or decor.

Darwi Terracotta is the same clay as Classic in an earthy terracotta shade. Because the color runs right through the block, a chip or a sanded edge shows the same tone as the surface, so an unpainted piece keeps its finish as it wears — the reason to choose it over painting Classic to match.

Good for: pots and vessels, tiles and plaques, garden and rustic pieces, and anything meant to read as fired earthenware without a kiln.

Drying. Darwi hardens at roughly 24 hours per centimeter of thickness, measured from the surface inward, so a solid piece an inch through wants the better part of three days. Let it dry slowly and evenly in the open air rather than rushing it with heat, and turn it now and then so the underside dries at the same rate as the top. It does not shrink as it dries, which is what makes it usable for pieces that have to fit something.

Once it is dry you can sand it, carve it, drill it and paint it. Acrylics take well. Air-dry clay is not waterproof on its own, so anything that will be handled, worn or exposed to damp wants sealing — Darwi Vernis is the maker's own varnish and we carry it in brush-on and aerosol, gloss, satin and matte.

Where air-dry is the wrong choice. Darwi is not polymer clay and does not behave like it. Thin, slender pieces are brittle once dry, it will soften again if it gets properly wet before it is sealed, and there is no way to re-work a piece once it has hardened. If you are making cutter earrings, fine canework, or anything thin that gets worn and flexed, an oven-bake clay such as Cernit — Darwi’s sister brand from the same factory — or Sculpey Premo or FIMO Professional is the better buy. Darwi comes into its own on sculpture and decorative work with some substance to it, and on anything large, where a kilogram of air-dry clay costs a fraction of the same volume in polymer.

Specification. 500 g (1.1 lb) loaf. Air-drying, no baking. Dries terracotta. Hardens at about 24 hours per centimeter of thickness. Does not shrink. Made in Belgium.