Picture Framing Glossary


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Absorbent (Absorbent Properties): This refers to paper products that absorb liquids such as water, ink, or paint. An example is blotting paper which is used to absorb access ink. Towels as well as mat boards are also considered absorbent.

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 Burn: Matting and backing board that is made from wood pulp fibers has naturally occurring acids and lignins.  If these materials are not chemically treated, the acid will 'leak' onto the artwork.  This 'leaking' is called acid burn and manifests itself in the yellowing and brittleness of the paper. Although chemically treated wood pulp matting and backing board will slow this process, to eliminate it, it is often best to use a 100% cotton based product. Since cotton is naturally acid free, it will not damage any artwork.

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.

Acrylite®: A trade name of a brand of glazing made by Evonic Industires (this link will take you outside of PictureFrameGuys.com)  

Adhesive: A material that is used to bond two materials. This can be glue, tape or a paste.

Adhesive MatBoards: See "Self-Adhesive Matboards"  

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.

Alkaline: Any organic compound that has a pH value greater than 7. See also "Acidic".

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.

For example, if a customer  orders an 14" x 17" frame, the molding will actually will be cut 1/8 inch longer to ensure a good fit. If it were cut to exactly 14" x 17", then it would be tough getting everything to fit.  Also, since wood is a natural product, it will expand and contract over time as humidity and moisture levels change. So in the case of wood products, an allowance is especially important to avoid bucking of the artwork.

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. In practice there are many levels of archiving ranging from what a typical framer will use in a retail store to the methods and materials curators will employ.

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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. In some cases, when this white bevel is not desired, the mat board can be inserted into the frame backwards, thereby having the white core face the artwork. Another solution is to purchase mat which has a core that is the same color as the outside.  Although more expensive, sometimes framers prefer this option.

Burnishing Bone: A burnishing bone is a small tool used in the framing industry. It has many purposes, but its main purpose is for fine finishing the rough edges caused by a cutting knife. It is also used to make creases in adhesive tapes and paper. The advantage of using a burnishing bone in such cases is that it does not cause the paper to loose its shininess. They are available in various sizes.

Brush: In order to remove stray particles from mats and artwork before closing the frame, framers often use brushes made of natural horsehair.Such brushes cost anywhere between $5 -$20 and are useful if a large volume of framing will be done. 

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Canvas: Canvas materials have been used throughout history to make everything from tents, to sails, to awnings, to needlework and in the framing industry, as a medium for oil and acrylic paintings. Canvas is classified in 3 ways: The first method is by measuring one square yard of its weight.  The other two methods used are by classifying the material's duck.

Artist Canvasis made of either cotton, linen, or a synthetic fiber.  It is stretched onto wooden frames and used as supports for paintings.  Artist canvas is available in several thicknesses from 7 – 10 ounces.  Generally, the heavier the fabric, the better the quality. However, it is also important to pay attention to coatings.  Many canvases are coated with several layers of gesso.  This can increase their weight by up to 40% - 50%. It is possible to purchase canvas either in rolls, or pre-stretched onto a piece of canvas. While rolled canvas is much less expensive, the trade off of course is that it must be stretched by the artest.  A time consuming endeavor for the beginner.

Certified Picture Framer (CPF): The Certified Picture Framer® is an accreditation given by the Photo Marketing Association International (PMA). The exam tests knowledge in 5 areas of picture framing, which are general knowledge, preservation, mechanical, mathematics and mounting. In 2010, the PMA site stated that just under 4,000 individuals worldwide were CPF certified since the program began in 1986.

Conservation Framing: See archival framing.

Corrugated Corners: These are hard cardboard corner pieces used to protect a frame and its corners during shipping, long-term storage or moving. When you purchase frames from the Picture Frame Guys, each frame is packaged with protective corrugated corners. We recommend keeping these as they can be reused with other frames.

*Cotton: Definition

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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.

Duck Grade: A duck,which is about 792 square inches, or 0.61 yards, is a method developed by the Dutch to determine the quality of either linen or canvas.It is still used today to determine the quality of canvas used for painting and printing.  (Note on printing: In the last 10 years, high quality printers have been developed which possess the technology to print on canvas.)

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.  Dust covers are most often used only with precious artwork when archival framing techniques are called for.

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Extrusion: This is the manufacturing process which is used to make metal frames.The aluminum is heated until it becomes liquid.  At this point, the molten aluminum is forced by pressure though a special die which provides a desired shape. Once the aluminum cools, it is heat treated to make it hard (to prevent bending and chipping) and then covered with several layers of primer and high quality paint.

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Floater Frame: This is a type of frame first introduced to the marketplace in the late 1990's.  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. Floater frames are available in both metal and wood designs.

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.

You can test this at home by taking 2 strips of paper, one 1 inch thick and the other 4 inches thick.  Cut each to a 45°angle and you will see that the 4-inch strip extends much further then the 1 inch strip.

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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 artowrk and the backing.  In most cases, it is 2mm or 3mm museum glass or 1/8" acrylic. The purpose of glazing is to protect the contents inside of a frame from dust and sudden shifts in temperature and humidity.  That is, the glazing will act as a buffer to slow sudden temperature and humidity changes which will decompose paper, canvas and other organic materials over time.It is highly recommended for precious or semi-precious items.

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Hardware: This includes all of the accessories required to hang a picture frame. It includes wires, spring and V-type clips and hangers (sawtooth, ring, etc.).  Metal frames require more hardware because the rails are attached not with glue and nails, but with special hardware made specifically for the task.

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.  We recommend hinging only from the top. This way gravity will pull the artwork down and it will be less likely to crinkle as it would if pushed from both the top and bottom.  If possible, it is also useful for the tape to tear easier than the artwork.  This way, if the artwork is pulled or otherwise stressed, the easily replaceable tape will tear before the artwork.

Hogarth or Hogarth Molding: The  

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Larson-Juhl: Originally a small Wisconsin Company  that sold simple and traditional wood picture frame molding. In the 1970's the company began offering a wider and wider range of styles, profiles and specialty finishes. Today, Larson-Juhl is among the premier molding wholesalers.

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.  They are very commonly used in framing oil paintings, which are often bigger than the maximum size of a 32"x40" mat board.

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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 joined by either glue, st

Metal Frame:
Metal frames are made of high quality extruded aluminum which is primed and painted with high quality paint.  One of the benefits of metal is it is available in many vibrant colors and many metallic finishes.  Examples include gunmetal, German silver, pewter and graphite. Just to name a few.

Miter Cut (Mitered): To make a picture frame, the moulding rails are cut at 45° angles which are joined by either glue, staples, nails or in the case of metal frames, specialty hardware. The first in many critical steps in building a quality frame, it is important for the angles to be perfect.  The saws and saw blades that framers use for this process are very precise pieces of equipment that can easily cost over $10,000 per machine.

Multiple Mats: This is a term used when more than one mat board is used.  While most matted frames are framed with single mats, in some cases, the artist decides to use two, three and in some cases more than 3 mats in order to give the piece more emphasis.  When many mats are used, the piece falls inside of the frame to the viewer's eye.

Museum Glass: Unlike glass used for the window of a house or building, museum glass is specially made transparent and thin glass. It is available in 2mm (about 1/16") and 3mm (about 1/8") thicknesses.  The thicker, 3mm glass is usually used for large framing projects. Because the thicker glass is stiffer, it is less prone to bending and distorting light as it hits the glass.  

Museum Quality Framing: See archival framing.

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Nielsen Profile (followed by a number): Nielsen Bainbridge is the largest maker of metal molding in the United States.  The company makes dozens of different metal molds in over 200 colors.  A Nielsen profile is identified by either a two or three digit number.  For example, you may see Nielsen Profile 11 listed.  This indicates that the profile number is 11. When browsing the metal frame section of this site, the Picture Frame Guys lists the Nielsen profile number in the light box pop up.

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Offset: (see mat offset)

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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.  Each ply is about 1/64" of an inch and are generally made in even numbers. Listed below are the thicknesses for up to 8 plys:

- 2 plys: 1/32"
- 4 plys: 1/16"
- 6 plys: 1/8"
- 8 plys: 1/4"

Profile: The curves and design of a frame. A picture frame's profile includes the height, width and rabbet, and come in a variety of shapes and sizes.

Putty: A special filler that is used on wood frames to create a perfect joint.

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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.

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Self-Adhesive Matboards: Matboards that have a pre-applied adhesive on them. The adhesive is usually either heat- or pressure-activated.

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.

Shape: While there are no hard and fast rules about frame molding nomenclature, certain ones do exist. Common shapes include flat, round, half-found, swan, reverse swan and embossed.

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.   

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Triple Mat: A framing technique in which three mats are used for emphasis. See multiple mats for more details.

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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.

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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.

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.

Wood Frame: The original: a frame that is made with any number of woods. These frames make up the bulk of the custom-framing industry and are available in a host of colors, styles and materials.