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 Roc is the tough one. Darwi describe it as reaching, once dried and sanded, “a strength comparable to that of marble”, and it takes a knock far better than the rest of the range. That shock resistance is exactly what delicate work needs — the thin, protruding parts that snap first on an ordinary air-dry clay. It dries slightly ivory rather than bright white; sand it back for a paler finish.

Good for: sculpture with fine or projecting detail, pieces that will be handled, and anything you would rather not have to repair.

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.

For a tall or fine-limbed sculpture, build over a wire armature. The clay grips it well and the frame carries the weight while the piece is still soft.

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. 1 kg (2.2 lb) loaf. Air-drying, no baking. Dries slightly ivory. Hardens at about 24 hours per centimeter of thickness. Does not shrink. Made in Belgium.