Picture Frame Anatomy: The Complete Glossary of Framing Terms
A reference guide to the parts of a picture frame and the language framers use
Picture framing has its own vocabulary, and most of it goes unexplained until you find yourself reading a quote with terms like rabbet depth, V-nail, and bumper pads. The terms describe specific parts of the frame, specific tools, and specific construction methods that all matter for how the finished piece looks and how long it lasts. This glossary covers the words you will run into when ordering a custom frame, talking to a framer, or troubleshooting a piece you already own. Each term has a short definition with enough context to use it correctly the next time it comes up.
Picture Frame Anatomy and Framing Terminology
These terms describe the shape and parts of the frame moulding itself, before any glazing, mat, or art goes into it.
Moulding
The decorative wood strip that forms the visible frame. Moulding comes in linear feet from the manufacturer and is cut and joined into a finished frame. In the wider industry the term also covers aluminum and other metal profiles, but solid wood is the material we build with. The moulding profile determines the look of the frame: traditional, contemporary, ornate, minimal, and everything in between.
Face
The front-facing surface of the moulding, visible when the frame is on the wall. The face is what you see when you look straight at the frame. Face width is measured from the inside edge to the outside edge of the front surface.
Lip
The inner front edge of the moulding that overlaps the artwork or mat board. The lip holds the contents of the frame in place and prevents them from falling forward. Lip depth typically runs 1/8 to 3/8 inch.
Rabbet
The L-shaped channel cut into the back inner edge of the moulding that holds the glazing, mat, art, and backing. Rabbet width determines what fits into the frame, and rabbet depth determines how thick the framing package can be.
Rabbet Depth
The vertical distance from the back of the lip to the back surface of the rabbet. A standard frame has 3/8 to 1/2 inch of rabbet depth, which is enough for glazing, a single mat, the artwork, and a backing board. Shadow boxes need much deeper rabbets, sometimes 2 inches or more.
Sight Size
The visible opening size of the frame, measured inside the lip. Sight size is always slightly smaller than the rabbet size because the lip overlaps a small portion of the contents. When you order a 16 by 20 frame, the sight size is roughly 15 3/4 by 19 3/4 inches.
Outside Dimensions
The total external measurements of the finished frame, including the moulding width on all four sides. A 16 by 20 frame with 2 inch wide moulding has outside dimensions of 20 by 24 inches.
Joinery Terms
These terms describe how the four pieces of moulding are cut and connected to form the finished frame.
Miter
A 45 degree angled cut at the end of each moulding piece. Two miters joined at right angles form a 90 degree corner with no end grain visible. Mitered corners are the standard joining method for picture frames.
Butt Joint
A joining method where one piece of moulding is cut square and butted against another square cut piece. Butt joints show end grain and are used for some floater frames and shadow boxes, but rarely for traditional picture frames.
V-Nail
A small V-shaped metal fastener driven into the back of mitered corners to hold them together. V-nails are inserted with a special tool that compresses them between the two moulding pieces. Two to four V-nails per corner is standard.
Underpinner
The pneumatic or mechanical machine that drives V-nails into mitered corners. Underpinners are the modern standard for frame assembly because they produce consistent, strong joints quickly.
Glue Up
The application of wood glue to the mitered surfaces before joining. Glue plus V-nails creates a much stronger joint than V-nails alone, and is standard for any frame meant to last.
Cut List
The list of moulding lengths needed for a given frame, accounting for moulding width and the 45 degree miter cuts. A 16 by 20 frame in 1 inch moulding needs two pieces at 18 inches and two at 22 inches, plus extra length for the miter cuts.
Glazing Terms
Glazing is the clear material that protects the artwork from the front of the frame. These terms describe glazing types and properties.
Glazing
The general term for the clear panel in the front of a frame. We glaze with framer's grade acrylic, which protects the art from dust, moisture, and physical contact while staying lighter and more shatter-resistant than glass.
Clear Acrylic
Standard framer's grade acrylic with a clear, optically smooth surface. It is the default glazing for most frames: lightweight, durable, and easy to ship without the breakage risk of glass.
Non-Glare Acrylic
Framer's grade acrylic with a lightly diffused surface that scatters reflections, so the art reads cleanly even in a brightly lit room. It is the alternative to clear acrylic when glare from windows or lamps is a concern.
Anti-Reflective Surface
A treatment that reduces surface reflections compared to plain glazing, making the panel read as nearly invisible from in front of the frame. The effect is what lets the art show without a mirror-like sheen bouncing back at the viewer.
Acrylic vs Glass Weight
Acrylic is roughly half the weight of glass at the same size, which is why it is the practical choice for large frames, frames in homes with kids, and frames that will be shipped. It is also lighter in color cast than glass, so it adds less tint over the artwork.
Mat Board Terms
The mat board is the colored or neutral border around the artwork, between the art and the frame. These terms describe mat parts and types.
Mat Window
The cut opening in the mat that exposes the artwork. The window is sized slightly smaller than the artwork so the mat overlaps the edges and holds the piece in position.
Bevel
The angled inside edge of the cut mat window. A standard mat bevel is cut at 45 degrees and is white or off-white in color, providing a subtle visual transition between the mat surface and the artwork.
Reverse Bevel
A bevel cut so the angle is hidden from the front view. Reverse bevels are used for special design effects and for double mats where the bottom mat color should be the only visible color.
Single Mat
A frame package with one mat board between the artwork and the glazing. Single matting is the most common matting style.
Double Mat
A frame package with two mat boards stacked, the top mat with a slightly larger window opening that reveals a thin border of the bottom mat. The bottom mat color shows as an accent line around the artwork.
Reveal
The visible portion of the bottom mat in a double mat package. Reveal width is typically 1/8 to 1/4 inch and is set when the mat windows are cut.
Acid-Free Mat
Mat board manufactured without acidic compounds, typically buffered with calcium carbonate to neutralize any future acidic gases that reach it. Acid-free mat is the standard for any framing that will last more than a few years.
Cotton Rag Mat
The premium mat board made from 100 percent cotton fiber. Cotton rag is naturally acid-free with no chemical buffering needed and is the longest-lasting mat material available.
Mat Hinge
A small piece of acid-free tape that connects the top edge of the mat to the backing board, allowing the mat to lift up like a book cover for inserting or removing artwork.
Fillet
A small decorative moulding placed inside the mat window opening, typically gilded or painted, that adds a fine accent line around the artwork. Fillets are common in traditional and ornate framing.
Backing Terms
The backing is the layer behind the artwork that supports it within the frame. These terms describe backing materials and parts.
Backing Board
The rigid panel that sits behind the artwork inside the frame. Backing boards provide structural support and a flat surface against which the artwork rests.
Foam-Core Board
A common backing material made from a foam core sandwiched between paper facings. Standard foam-core works for decoration framing. Acid-free foam-core is used for conservation work.
Acid-Free Corrugated
A multilayer corrugated cardboard made from acid-free fiber, used as a final back layer in conservation frames to prevent acid migration from any wall surface or hanging hardware.
Dust Cover
A thin paper sheet glued to the back of the frame after assembly. The dust cover seals the frame package against airborne dust and insects entering the rabbet from behind.
Bumper Pads
Small felt or cork pads adhered to the bottom back corners of the frame. Bumpers hold the frame slightly away from the wall, allowing air circulation and preventing wall scuffs.
Mounting Terms
Mounting is the method used to attach the artwork to the backing board. These terms describe mounting techniques and materials.
Hinge Mounting
The conservation standard mounting method, using small strips of acid-free tape or paper to attach only the top edge of the artwork to the backing. Hinge mounting allows the piece to expand and contract freely with humidity changes.
Japanese Hinge
A hinge made from mulberry paper (kozo) and wheat starch paste. Japanese hinges are fully reversible and are the standard for conservation framing of works on paper.
Dry Mount
A mounting method that uses heat-activated adhesive tissue to permanently bond the artwork to a rigid board. Dry mounting is fast and produces flat, smooth results, but it is not reversible and is unsuitable for conservation work.
Float Mount
A mounting style where the artwork sits visibly above the mounting board with all four edges showing, rather than being hidden under a mat window. Float mounting is used for deckle-edge papers, Japanese woodblock prints, and any piece where the edges are part of the design.
Spacer
A thin strip of acid-free material placed inside the rabbet between the glazing and the artwork to prevent direct contact. Spacers are essential for pastels, charcoal drawings, and any work with surface texture that must not touch the glazing.
Sink Mat
A custom backing built up with layers of acid-free board around the artwork to hold it in place without any adhesive. Sink mats are used for fragile or three-dimensional pieces that cannot be hinged.
Corner Pocket
A small triangle of acid-free Mylar adhered to the backing board, into which the corners of the artwork slip. Corner pockets hold the artwork without any adhesive ever touching the piece.