Judging veneer quality

Why you check before cutting

Veneer is a natural product. Every sheet has its own colour, figure and history, and not every property shows at first glance. In intarsia, many small pieces are cut from one sheet, so a split, a loose knot or a thin spot ends up in exactly one piece, and that piece decides the whole work.

So every sheet is checked before the first piece is cut. It takes a few minutes; a fault that only shows after pressing can hardly be put right, because the piece is fixed to the substrate.

Checking in the right light

Two kinds of light show different faults. Raking light, a lamp shining low across the sheet, shows waves, bumps, knife marks and surface checks as shadows. Backlight, holding the sheet against a window or lamp, shows splits and holes that go right through: light shines through them.

Colour, on the other hand, is judged in even, neutral light, ideally the light the finished piece will be seen in. How raking light helps on the finished piece too is described in checking the quality of an intarsia.

Thickness and evenness

The nominal thickness on the label is a guide. Measure with calipers at several places, at least at all four corners of a sheet. A sheet that is clearly thinner on one side than the other was sliced unevenly or has distorted while drying.

For intarsia, the comparison between woods matters more than the number itself. Two species that lie side by side should be the same thickness; as little as 0.2 mm gives a step after pressing that has to be sanded away and costs sharpness. Which thicknesses are usual, and for what, is covered in veneer grades and supply forms.

Splits, holes and knots

End splits sit at the short ends of a sheet, where the wood loses moisture fastest while drying. They run along the grain and can tear further when cutting, so the end is usually trimmed off with a margin rather than used for pieces. With woods prone to splitting, such as wenge, check the long edges closely too.

Knots are not a defect in themselves. A sound, tight knot is part of the wood and can make a piece lively; a loose knot, or one with a black ring around it, easily breaks out when cutting or sanding. In intarsia you can place a sound knot deliberately in one piece or cut around a bad one.

Photo: Reihax

Holes, from fallen-out knots or insects for instance, show in backlight. They are only harmless if you can safely avoid them when cutting.

Flatness and cockling

A good sheet lies flat on the table. Cockled sheets come from uneven drying, from storage rolled up or without weight, and from wood with restless grain such as burr or strongly figured crown cut. Slight waves can often be fixed: dampen the sheet lightly and let it dry between clean boards under weight.

Strong cockling is a warning. A piece that does not lie flat while you cut slips under the knife, and a surface that was not flat before pressing tends to build up tension later. How to store veneer so that it does not cockle in the first place is described in storing veneer.

Colour, sapwood and stains

Colour always varies a little within a species. It becomes critical when pieces of the same wood lie side by side and one looks clearly lighter or darker, so all the sheets meant for one piece are laid out and compared first.

• Sapwood: many dark woods have light sapwood at the edge of the trunk. In walnut it is much lighter than the heartwood, so a sheet with a sapwood edge gives you two colours, not one.
• Stains: water marks and mould stains come from damp storage. They often lie deeper than the surface and cannot be sanded out.
• Light damage: the top sheet of a stack that lay in the light for a long time is bleached or darkened at the surface. The difference from the sheets below only shows after sanding.

Grain and the run of the fibres

For small fields and straight edges, calm, straight grain is the most predictable: the knife follows the fibre, and light is reflected evenly across the surface. Strongly moving grain, interlocked grain or swirls are beautiful but need more care when cutting and sanding, because the fibres run in changing directions.

Photo: Reihax

It also matters how the grain suits the planned shape. A sheet can be flawless and still wrong for a particular piece, because its figure runs across the direction you want (grain direction). How the cut shapes the figure is explained in types of veneer and cuts.

Photo: Reihax

The loose and the tight side

Sliced veneer has two different sides. While being sliced, the leaf bends over the knife, and the side that is stretched gets fine checks across the grain: that is the loose side. The other, the tight side, stays smoother.

You can tell them apart by gently flexing the sheet both ways: when the loose side curves outwards, the fine checks open up. In raking light it also looks rougher. For the show face you usually choose the tight side, because it sands more calmly and takes the finish more evenly. In book-matched pictures the side changes from leaf to leaf, which has to be taken into account when planning.

Job lots and veneer of unknown origin

Not every veneer comes with a label. Job lots from workshops closing down, estates or warehouse sales are often cheap and sometimes excellent, but the species, age and storage are unclear. For intarsia, which works with small pieces, such a lot is often worth it if you check it thoroughly:

1. Judge the species from the wood itself: colour, pores, weight, the smell when sanding. Trade names only help so far.
2. Measure the thickness on several sheets; lots are rarely uniform.
3. Look for stains, light damage and brittle, crumbly edges that point to storage that was too dry or too damp.
4. Cut a test piece and make a finished sample before the lot goes into a real piece.

The Reihax mahogany is such a case: it came from a workshop closing down and was sold as mahogany without a botanical name. What can be said about this wood is therefore based on what the veneer itself shows (mahogany).

Checklist before the first cut

• Thickness measured at four points, all the woods of one piece the same thickness
• No splits or holes right through, in backlight, in the areas you will use
• End splits marked and trimmed off generously
• Knots sound, or avoided on purpose
• The sheet lies flat or has been flattened
• Colour of all sheets of one species compared side by side, sapwood spotted
• Tight side marked as the show face
• Grain direction planned for every piece