Acid: Any material that has a ph-Value of greater than 7 (on a 0 – 14 scale). The acid content of a product can be tested in various ways. One of the easiest is by using litmus paper.

Acid-Etched: A process in which a material is engraved by allowing an acidic solution to dissolve on it’s surface. In picture framing, this process is used when creating non glare glazing. The manufacturer will briefly apply a mild acid solution to the acrylic or glass which will roughen the surface. This in turn disperses light as it hits the glazing, thereby reducing glare.

Acid-free: Acidity is measured by determining the pH-value of a material.  The pH scale ranges from 0 to 14, where 0 is totally acid and 14 is totally alkaline. Pure water at 77°F is very close a pH of 7, which is pH neutral because it falls exactly between 0 and 14. Wood, from which matting, cardboard and backing materials are made, is naturally acidic and is chemically treated to reduce or at least suppress acid levels. Cotton on the other hand is much closer to a pH value of 7.  Therefore, cotton products, often called Ragmat, are considered to be acid-free and will be less likely to cause acid burn.

Acid-free Paper / (also Acid-Free Matting): In framing this refers to a product that is close to a PH of 7. In reality, it is impossible for a natural product to be totally non-acidic as this would result in the material disintegrating (because the fibers would not stick to one another). Some cottons have pH values that are very close to 7 and are marketed as “acid-free”.

Acrylic: Commonly used as a replacement for glass, acrylic is a hard synthetic polymer material made from derivatives of acrylic acid. There are many variations of acrylic, but the most common one is known as poly-methyl methacrylate (or PMMA) and it is best known under the trade names Lucite®, Plexiglas®, Perspex® and Crystallite®. Since it is easy to bend, cut and form, PMMA is used on everything from airplane windshields, to skylights to picture frame glazings.

Adhesive Release: A solvent that is used to chemically separate two compounds. In framing this is usually separating artwork from either a backing material, matting or mounting tape.

Allowance: This is a term which refers to the amount of length that is added to a frame when it is cut. It is done in order to ensure that the various frame components (mounting board, matting and glazing) will easily fit into a frame.

Alpha Cellulose: This compound is the major compound found in wood pulp and it is what gives wood an acidic pH-value. As a result, anything made with paper will be slightly acidic. Over the past 30 years the framing industry has made great strides to chemically treat wood pulp to make almost acid-free matting and backing materials. To read more about this, we refer readers to the Boston Museum of fine Art’s in-depth explanation of cellulose.

Archival Framing: Also called conservation framing, this is a widely used term in the framing industry. While there are no set industry-wide rules or standards, it is generally assumed that ‘archival’  implies the use of acid-free materials during the framing process.

Beveled Edge: A bevel is a sloping edge or surface. A framing standard is to cut the inside edge of a mat board at a 45° angle, or bevel. The center of most mats is white, and it is due to the angled cut that what we see the white core of the matboard. One of the benefits of this beveled edge is that the white core provides a border between the mat and the artwork thereby drawing the eye towards the artwork.

Corrugated Corners: These are hard cardboard corner pieces used to protect a frame and its corners during shipping, long-term storage or moving.

Double Mat: Often more than one mat is used in a frame. If two mats are used, the arrangement is called a double mat.  In this case, the inner mat (the one closest to the artwork) is usually an accented color and its border is only slightly revealed behind the outer mat mat.  Double mats are used to highlight a color in a work of art and focus the viewers eye towards the artwork.

Dust Cover: A seal typically made with craft paper which is stuck onto the back of a picture frame in order to prohibit dust from entering the frame from behind.

Floater Frame: It is a frame into which a canvas is placed from the front and attached from the back.  A small gap, perhaps 1/8″ or 1/4″ of an inch is left between the canvas and the frame lip. The floater frame derives its name from the fact that the canvas appears to be floating inside of the frame.

Foam Core: The material onto which artwork is mounted for framing. This material is relatively light and is commonly available in white and black. Though it is quite stiff, it cuts easily and is not prone to denting or accidental bending.  High quality foam core is acid-free and will not yellow the artwork over time.

Frame Size: A frame is measured from the molding’s inside corner to inside corner.  This is the size of the artwork, minus any calculated mat offset. The thicker a frame’s molding, the longer the outside corners will be.

Gesso: This is a glue-chalk primer which is typically applied to surfaces such as canvas in preparation for painting.  Gesso dries hard and is available for purchase in art supply stores.

Glazing: Any transparent material that is placed on the outer most edge of a frame (usually glass or plexiglass), in front of the matting, the artwork and the backing. The purpose of glazing is to protect the contents inside of a frame from dust and sudden shifts in temperature and humidity.

Hardware: This includes all of the accessories required to hang a picture frame. It includes wires, spring and V-type clips and hangers.

Hinging: The process of adhering artwork to the back of the mounting board. Acid-free tape or adhesive strips are attached to the top of the artwork.

Linen Liner: This is a filler used to create a small air gap between the artwork and the glass when matting is not used. Most of the time the linen liners are a neutral or white fabric material.

Mat Board: A paper material that protects the artwork from coming into contact with the glass and provides an aesthetically pleasing border to draw the eye to the center. Mat board is available in acid-free and also in specialty designs. It comes in a variety of densities; of course the thicker it is, the more the core will be exposed in the window.

Mat Grade: Mat’s generally come in three broad quality grades. The first is a very low grade mat board that can be used for short-term framing projects such school projects. The second grade is suitable for artwork that is expected to last 10-20 years. Finally, the 3rd grade is suitable for heirloom or precious pieces.

Mat Layers: Layering mats is the process of placing mats one on top of the other inside of a frame. This is often done with different colors of mat in order to accent the artwork.

Mat Offset: This is an industry term which refers to the amount of length which is subtracted from the artwork’s dimensions (height and width) so that the artwork will fit behind a mat. Typically either 1/8″ or 1/4″ of an inch is used from each side.

Mat Size: the mat size refers to the total height and width of a mat.  Unlike the mat window, which is only the opening in the mat through which the artwork is viewed, the mat size is the total size of the mat. This includes the mat window and the mat borders.  This is an important calculation for many reasons, one of which is determining the total size of a mat.  Mats of all grades, colors and textures are readily available in 43″ x 40″ dimensions. There are a smaller amount of colors available in 32″ x 40″ dimensions.

Mat Window (also Mat Window Opening): To make a wooden frame, the rails are cut at 45° angles which are usually joined together by glue.

Plexiglas: One of many trade names for acrylic.

Ply (4-ply, 6-ply, etc): This is a measure of thickness used for mat boards and mounting boards.The more plys, the thicker the board.

Rabbet: The inner lip of a frame in which the framing materials, including glass, mats, artwork, and backing are held.

Rail: A rail refers to the sides of a frame. A frame is composed of four rails.

Reversibility: In archival and museum quality framing, this term implies that the preservation methods used on a frame should be reversible. This ensures that any archival process can be undone.

Shadow Box: This is a framing technique in which three dimensional objects are framed.  We have seen objects ranging from ballet shoes to hockey pucks framed in shadow boxes.

Spacer: A spacer is a small usually plastic strip which is placed between the artwork and the glass and hidden under the frame’s lip. Spacers are used when matting or linen liner is unneeded or infeasible.  Spacers are also very useful in creating shadow boxes since they can put up to an inch gap between the mounting board and the glass, thereby providing a lot of room for the 3D object.

Triple Mat: A framing technique in which three mats are used for emphasis.

Window: The opening cut in a mat board through which the image can be viewed. The window is commonly in the exact center of the mat, but can be positioned elsewhere (higher or lower) to achieve specific viewing characteristics.

Weight Mat: A weighted mat has a bottom dimension that is taller than the other three sides. Weighted mats can be subtle or dramatic. The more weight one adds to the bottom of the mat, the more dramatic and contemporary the effect.

V-Groove: A v-shaped incision in the surface of a mat board that reveals the core and acts as a decorative border. V-grooves should be cut approximately 5/8″ away from the window.