Construct mold: position 1 wood-grain texture mat in bottom-right corner of one 15-by-20-inch piece of plywood; secure underside of mat with carpet tape. Repeat with remaining 3 mats and plywood pieces.Assemble 4 plywood boards at right angles according to the desired vessel shape: horizontal for a lower, wider container, or vertical for a taller, thinner container. Align mats inside so there are no gaps between them; 1 end of each plywood piece will extend beyond box.Using drill, secure plywood where 2 boards intersect perpendicularly, inserting 2 wood screws per side. Attach 20-by-20-inch piece of plywood to bottom of box, using remaining 4 wood screws. Coat mold interior with mold-release spray.
Fill mold: prepare hypertufa mixture (see "Basic Hypertufa How-To"): Wearing gloves and dust mask, mix 16 quarts peat moss, 16 quarts perlite, and 16 quarts Portland cement in a large, shallow bin. Add water gradually until mixture has the consistency of yogurt (to show the wood-grain texture better).Pour mixture into mold to a 2-inch depth. Set interior mold inside, centering it (you can fill it with sand to steady it). Continue adding mixture between vessels. Tap exterior with rubber mallet to minimize bubbles. Cover with plastic.
Finish hypertufa: Let set for 36 hours, then gently remove interior container. After another 12 hours, unscrew wooden mold to remove hypertufa. After removing mold, drill several holes into the bottom of vessel using a masonry bit, for drainage; smooth the top edge of pot with a planer file. Wrap it with plastic, and let cure for several weeks (a month is best).
Four 12-by-16-inch rubber texture mats, in wood-grain pattern (PA 02-4), $12, from Chinese Clay Art, 408-343-3919.
Four 15-by-20-inch pieces of 1/2-inch-thick plywood
Carpet tape (No. 50-605), by Roberts from Home Depot, 800-553-3199.
Drill with regular and masonry bits
12 wood screws
20-by-20-inch piece of 1/2-inch-thick plywood
Universal Smooth-On Mold Release (No. 66MR1), from the Compleat Sculptor, 800-972-8578.
Peat moss (No. 809383), by Miracle-Gro; Gray
Perlite, (No. 809352), by Miracle-Gro; Gray
Portland cement, from Home Depot, 800-553-3199
Interior mold (or construct one from cardboard, wrapping it with duct tape)
Sheet of plastic
Surform Plane Type, regular cut blade (No. 185515), by Stanley from Home Depot, 800-553-3199.