While most decorative panel manufacturers in North America will offer proprietary or custom grades, the consensus grading standard is ANSI/HPVA HP-1-2004, American National Standard for Hardwood and Decorative Plywood. This document establishes unique characteristics for each species of wood veneer in face grades of AA, A, B, C, D & E and in back grades of 1, 2, 3 & 4. This standard also provides standards for core grades and adhesives, and is a valuable resource for anyone buying or specifying decorative wood panels. ANSI/HPVA HP-1-2004 is available from the Hardwood Plywood & Veneer Association, P.O. Box 2789 Reston, VA 20195, 703-435-2900.
What follows is a general description of the grade categories from the HPVA. For details about individual species refer to the standard.
FACE GRADE APPLICATIONS
- AA: a premium face grade for exclusive uses such as architectural paneling and interiors, case goods and quality furniture.
- A: where AA is not required, but excellent appearance is still important.
- B: where the natural characteristics and appearance of the species are desirable.
- C: allows for unlimited color and increased natural characteristics and is perfect for applications where an economical panel is needed.
- D&E: provide sound surfaces but allow unlimited color variation and allow repairs in increasing size ranges. Applications: where surface will be hidden or a more rustic character is desired.
BACK GRADE DESCRIPTIONS
Back Grades are designated by numbers 1,2,3 and 4. Requirements of Grade 1 are most restrictive, with Grades 2,3 and 4 being progressively less restrictive. Grades 1 and 2 provide sound surfaces with all openings in the veneer repaired except for vertical worm holes not larger than 1.6mm (1/16″). Grades 3 and 4 permit some open defects, however grade 3 can be obtained with repaired splits, joints, bark pockets, laps and knotholes to achieve a sound surface if specified by the buyer. Grade 4 permits knot holes up to 102mm (4″) in diameter and open splits and joints limited by width and length.
In addition to the wood’s specie, how it is cut from the log determines its appearance. There are two basic methods: Rotary cutting and Slicing, though many variations on sliced veneers yield very different appearances.
Rotary veneers are peeled from a log like paper coming off of a roll, though the veneers are not truly continuous. This method produces large pieces of veneer with very flat, random grain patterns. As the wood is peeled from the outside to the center of the log it moves from sapwood to heartwood which can be very different in color. Heartwood and sapwood may be combined in one piece of veneer. The advantage of rotary veneers is that it is generally the least expensive cutting method, and can provide large pieces of veneer and “whole piece faces”. The disadvantage is that rotary veneers can have a bland appearance and may vary widely in color within the same panel though this can be specified out. Not all species of wood produce logs that can be rotary peeled and decorative softwoods are rarely rotary peeled.
Sliced veneers are produced from a log that has been prepared by cutting it into “cants”, or large blocks. How these cants are cut and their orientation to the veneer knife will produce unique grain patterns from different wood species.
- PLAIN SLICED veneers are cut along a log’s growth rings and typically present a cathedral grain pattern and pieces of veneer or “flitches” 6″ to 12″ wide. Plain Slicing produces the highest yield and is generally the least expensive slicing method. Half Round produces a similar pattern and size.
- QUARTER SLICED veneers are cut perpendicular to a log’s growth rings and generally produce straight grained veneers. In many species this will reveal decorative figure in the wood like flake patterns in white oak. Quarter slicing produces smaller veneer flitches and is more expensive.
- RIFT CUT is general reserved for oak and is intended to produce a straight grain without exposing the flake pattern. Rift cutting is at a tangent to a log’s growth rings.
Other than rotary cut whole piece faces, all veneers for full sized panels must be assembled into large sheets or “spliced” together. How the individual veneer flitches are arranged is called veneer matching, and will produce a specific pattern in the finished panel. Veneer matching should not be confused with panel matching which refers to the relationship between several panels in a sequence, as in a large auditorium.
Book Matching is the most common matching method in which every other flitch of veneer is turned over like the pages of a book. The result is a pleasing symmetrical pattern of mirror images of grain. While this is a popular technique, one drawback is that one side of the veneer flitches will absorb stains and finishes at a different rate from the other and can produce a “Barber Pole” effect of dark and light. Careful finishing can minimize this effect.
Slip Matching sequences veneers without turning the flitches, like sliding a deck of cards. This allows the grain pattern of each flitch to repeat across the face of the panel, improving color uniformity. With straighter grained veneers the joints won’t be prominent, but some rotary cut veneers, especially those that include both heart and sap wood, can highlight the flitch joints.
Pleasing Match veneers are selected for uniformity of color without regard to grain pattern. No sharp color contrast is allowed, but grain patterns may not match.
Random Matching assembles veneer flitches without regard to grain pattern or color. Visual continuity is not guaranteed, though some species are naturally more uniform than others.