# Black walnut moves evenly, works cleanly and suits oil; keep its pale sapwood off show surfaces Hewn Shop Notes · https://hewn.build/shop-notes/the-walnut AI-drafted, not yet checked: Drafted by Chip, the writing system Hewn runs on Claude, from Hewn's craft corpus. Jonathan Salomons has not read this note yet, and no outside reader has checked it. Read it as a shop note: check a number before you cut to it. Cite as: "Black walnut moves evenly, works cleanly and suits oil; keep its pale sapwood off show surfaces." Hewn Shop Notes, hewn.build/shop-notes/the-walnut. Drafted 2026-03-15; AI-drafted, not yet checked. --- Black walnut is a cooperative furniture wood. Its tangential-to-radial shrinkage ratio is about 1.42, low among furniture hardwoods, so it moves more evenly than most. It planes and chisels cleanly with a sharp edge. Its pale sapwood contrasts sharply with the dark heartwood and should be kept off natural-finish show surfaces [1][3][4]. ## Sapwood Black walnut sapwood is pale cream to yellow-white. Walnut heartwood is chocolate brown. The contrast between them is among the sharpest of any domestic furniture species [3]. Cherry sapwood blends with the heartwood at first and diverges only as the heartwood darkens. Walnut sapwood shows against the heartwood immediately under finish and does not improve with time [3]. On a natural-finish walnut piece, exclude sapwood from visible surfaces rather than trimming or blending it [3]. Read the end grain of a walnut board before buying. The sapwood is the pale outer zone. Some boards carry it on one edge and others on several [3]. Mark the sapwood boundary on a walnut board before milling, not after, and plan the cuts to keep the marked material off show surfaces [3]. Walnut sapwood has the same hardness and grain behaviour as walnut heartwood. Its difference is visual, not structural [3]. Walnut sapwood suits drawer box sides and other secondary parts with no show surface. A drawer with sapwood sides and a heartwood front is sound and costs less than an all-heartwood drawer [3]. ## Movement Black walnut's total tangential shrinkage, green to oven-dry, is about 1.42 times its radial shrinkage. Black cherry's ratio is about 1.92, white oak's about 1.88 and hard maple's about 2.06 [1]. Among black walnut, black cherry, white oak and hard maple, black walnut has the lowest tangential-to-radial shrinkage ratio [1]. A low tangential-to-radial ratio means a board shrinks and swells more evenly in both directions and is less prone to cupping. It does not by itself mean the smallest movement across the width [1]. Seasonal movement across a board equals width × C × the moisture content swing in percentage points. C is the dimensional change coefficient per 1% change in moisture content: tangential for flat-sawn boards, radial for quartersawn boards [2]. Black walnut's dimensional change coefficients are 0.00274 tangential and 0.00190 radial, per 1% change in moisture content. White oak's are 0.00376 and 0.00194 [2]. Worked example: a 24-inch flat-sawn black walnut panel through a 7% moisture content swing moves 24 × 0.00274 × 7 = about 0.46 inch, roughly half an inch, across its width [2]. Worked example: a 24-inch flat-sawn white oak panel through the same 7% swing moves 24 × 0.00376 × 7 = about 0.63 inch across its width [2]. Because walnut's tangential and radial coefficients are close, quartersawn walnut gains less over flat-sawn walnut than quartersawn white oak gains over flat-sawn white oak. A wide flat-sawn walnut panel is a practical choice where wide flat-sawn white oak would call for quartersawn stock [1][2]. A wide walnut panel still needs movement allowance: breadboard ends with room to move, and floating panels [2]. ## At the bench Walnut grain runs straight to slightly interlocked. A sharp iron at standard settings planes it cleanly in both directions, with less grain reversal than bigleaf maple [4]. Walnut dulls edge tools faster than cherry and slower than bigleaf maple. Start a session of show-surface smoothing on walnut with a freshly sharpened edge [4]. Walnut end grain is dense, fine and even. It trims cleanly on a shooting board, and a sharp chisel registers cleanly at baselines and shoulder lines [4]. A dull chisel in walnut end grain crushes the fibres instead of cutting them, leaving a joint that looks tight but has a poor glue surface [4]. ## Gluing walnut Natural oils in black walnut can migrate to a machined surface that has been left to sit and reduce glue adhesion. For critical joints, mill the mating faces fresh and assemble promptly [5]. When a walnut joint cannot be re-milled before gluing, wipe both mating faces with naphtha and let them dry fully before applying glue. The solvent removes the surface oil layer [5]. Teak needs a solvent wipe before gluing as standard practice. Walnut follows the same fresh-surface principle at a lower threshold [5]. ## Finishing walnut Penetrating oil finishes, such as hardwax oil, danish oil and pure tung oil, are a natural match for walnut. The oil enters the open pores rather than bridging them and brings the heartwood's warm colour forward [6]. A penetrating oil finish on walnut builds no film, can be maintained without stripping, and does not produce a high gloss [6]. Film finishes such as oil-based varnish and lacquer are fully compatible with walnut. For a smooth, glassy film surface, fill the open pores with grain filler before the first coat [6]. A waterborne finish applied over unfilled walnut pores can give a grey or flat cast. Fill the grain first, or apply a dewaxed shellac wash coat as the first layer [6]. A dewaxed shellac sealer coat under a film finish on walnut deepens the colour. Try it on a test board first [6]. Staining walnut to imitate another wood rarely improves it. Its natural colour and figure are its main value [6]. ## Supply and cost in British Columbia Black walnut does not grow natively in British Columbia. BC supply comes from eastern Canada and the United States, so availability is intermittent [7]. Walnut is priced at the top of the domestic furniture wood range in BC. Find a yard that stocks it consistently and buy ahead of the project when good stock arrives [7]. Walnut's cost suits pieces where the wood's colour and figure are the point, such as a simple form under a careful oil finish, over complicated pieces where the construction competes with the grain. ## Walnut is not a difficult wood Black walnut does not demand special skills. The planing, chiselling and joinery skills used on cherry and oak work on walnut. ## Sources 1. USDA Forest Products Laboratory, *Wood Handbook: Wood as an Engineering Material* (FPL-GTR-190), Chapter 4, Table 4-3 (shrinkage values), as listed in Reed's research note "Shrinkage Anisotropy", 2026-04-22. 2. USDA Forest Products Laboratory, *Wood Handbook* (FPL-GTR-282), Chapter 13, Equation 13-3 and Table 13-5, dimensional change coefficients, valid 6 to 14% moisture content (as listed in Hewn's notes, entry HEU-R735). 3. Hewn heuristic data, Reed entry HEU-R575 (black walnut sapwood exclusion), sourced in the entry to "species behavior; established cabinet-making practice", unreviewed. 4. Hewn heuristic data, Reed entry HEU-R578 (black walnut at the bench), sourced in the entry to other Reed entries and "species behavior", unreviewed (same note as source 3). 5. Hewn heuristic data, Reed entry HEU-R576 (black walnut oils and glue adhesion), sourced in the entry to "adhesive chemistry; species behavior; established practice for oily hardwoods", unreviewed (same note as source 3). 6. Hewn heuristic data, Reed entry HEU-R577 (black walnut finishing routes), sourced in the entry to other Reed entries and "species behavior", unreviewed (same note as source 3). 7. Hewn heuristic data, Reed entry HEU-R579 (black walnut BC sourcing), sourced in the entry to "species distribution; supply chain reasoning; established BC hardwood supply context", unreviewed (same note as source 3).