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Acid-Free refers to paper-based materials that do not contain free acid and have a pH value of 7.0 or higher at the point of manufacture. These materials may, however, become acidic over time due to a lack of buffering agents (Alkaline Reserve) and the presence of Lignin (a component of low-quality paper) or certain additives.

Acid Migration is a process that occurs when acid transfers from a material containing higher acidity levels to one containing less or no acidity. This may occur through off-gassing (gaseous transfer) or physical contact.

Adhesive Binding is type of binding in which single leaves are secured together solely with an adhesive applied to the textblock's spine edge. Animal glues, polyvinyl acetate (PVA) glues, and hot melt adhesives have all been used in the past for this type of binding, sometimes refered to as "perfect binding". Sections with perforations along the folds (or adhesive penetration into the folds to hold each section together) is also a type of adhesive binding, commercially known as perfo-, burst, mecha-notch, or perfopunch binding. See also Double Fan Adhesive Binding.

An Alkaline Reserve is a substance (commonly a calcium or magnesium salt) that has been added to the paper matrix either during manufacture or after, which neutralizes active acids and reduces the potential for the embittlement of paper. Papers that have an alkaline reserve are referred to as Alkaline Buffered.

Archival and Archivally Sound are terms that imply that a material or product is permanent, chemically stable, and durable. However, there is no standard by which a material can be referred to as "archival". Therefore, terms such as acid free, pH neutral, alkaline buffered, or lignin free may be better guides for the permanence of a material.

Archival Papers (such as Permalife, Perma/Dur, or archival tissues) are made of high quality paper fibers and frequently have an alkaline reserve (pH 8.5). They are used for interleaving sheets between acidic documents, for tabs for forms placed in contact with archival materials, and to make simple wrappers when more protection is desired than interleaving. It is important to use archival paper for preservation photocopying or for the printing of new publications.

A text that has Artifactual Value is important as a physical object, in addition to (or rather than) being important for the information it contains. Examples of this include copies of books signed by the author, original photographs, marginalia by famous owners/researchers, and highly decorative bindings.

Barrier Sheets are pieces of archival paper inserted in a book or placed between documents to prevent the transfer of media, acids, or damaging gases from one material to another. See also Interleaving.

Backing is the process of shaping a ridge or shoulder on each side of the spine of a text block after rounding it, and prior to lining it. Backing accommodates the thickness of the boards, and provides a hinge along which they swing. Backing also helps to prevent the spine of the text block from collapsing into a concave shape over time. See also Rounding.

Board is a general term used for any stiff material used to form the foundation for a book's case. They are made of various pulped or laminated fibrous materials pressed into large, flat sheets, which are then cut to size and covered with book cloth, buckram, leather, paper, or other materials, to form the case. The boards are referred to separately as the front and back boards.

Book Cloth is specially prepared cloth material used as a covering material for the case. It is a thin, woven cloth that has been dyed, filled, impregnated or coated with some compound, and subjected to heat and pressure. Book cloth falls into three main categories: starch-filled, acrylic-, pyroxylin-, or vinyl-impregnated, and plastic coated. Book cloth is lighter weight than buckram and is available in a range of grades and colors.

Boxes are containers used to hold loose sheets, documents, maps, or fragile books. Commercially available and hand-made boxes are constructed of many different materials and in many styles, including light-weight 4-flap boxes, heavier phase boxes, and sturdy clam-shell/drop spine boxes.

Bristol Board is a high quality heavy weight paper, sometimes made with cotton fiber prepared or glued together, usually with a caliper thickness of 0.006" and up.

Brittle Paper occurs when acidity increases causing the molecular structure of the cellulose fibers to weaken. This results in paper with reduced fold-endurance which breaks easily when it is bent or folded.

Buckram is a heavy-weave cotton cloth filled, impregnated, or coated with different compounds (mainly, starch and pyroxylin but also other materials) to enhance body, finish, and durability. Most bindings from library commercial binders have buckram cloth. C-Grade buckram is a thinner, smoother cloth than F-Grade buckram, which is heavier and the most durable.

The Case of a book consists of two boards, a spine inlay, and covering material (usually book cloth, buckram, paper, or leather). The case is made separately from the text block and is later attached to it in a step called Casing-In. See also Cover.

Case binding is a method of binding in which the case is made separately from the textblock and later attached to it. (As distinguished from leather bindings where the cover is assembled on the book.) The textblock is attached to its case by means of its endsheets and an adhesive. This method is used for most in-house book repairs and commercial bindings

Case Repair: A repair performed in-house to restore an original hard-bound cover when the only damage it has sustained is a torn or damaged spine.

Casing-In is the action of applying adhesive to the outermost endpapers of a text block and fitting the text block into its case.

Coated paper is a type of paper coated with white clay or a similar, synthetic substance to provide a smooth surface for printing detailed illustrations. The finish is often glossy but can be dull. Most popular magazines are printed on coated paper.

To Consolidate a spine is to attach the loose gatherings on spine edge of the text block to each other and to a cloth support using an adhesive.

The Cover of a book is a more generic term than case, used to imply any protective covering used on the outside of a book. Covers may be built onto the book (including laced-on boards and tight-back leather bindings), can be built separately from the textblock (including most modern cases), or be of simple, paperback construction.

Deacidification is a process that impregnates paper with an alkaline reserve to neutralize the active acid in the paper substrate and act as a buffer to neutralize acids produced in the future. Deacidification lengthens the life expectance of paper several times its ordinary life.

Disbinding is the action of removing the textblock from its cover or binder by easing the endsheets away from the textblock and by slitting the super (if present) with a scalpel.

Double Fan Adhesive Binding is a type of adhesive binding where the spine margin of each leaf in an unglued textblock is exposed 1/16" or less for an application of adhesive. The margin is exposed on both sides of each leaf by clamping the textblock on a vise-like press and then pushing against the textblock, first in one direction, then the other, thereby fanning or separating the edges of the leaves.

Encapsulation is process of creating a protective enclosure for flat materials by placing the object between two sheets of polyester film and then sealing it on at least one, but often all four edges using double sided tape, heat, or ultrasonic energy.

End Papers are the pages at the beginning and end of a volume added to both protect the textblock and to secure it into the cover. End papers include both paste-downs and flyleaves.

Flat back (sometimes referred to as square back) is a textblock that has not been rounded or backed.

Flyleaf is the leaf (or leaves) forming that part of the folded endsheet not pasted down to the inside of the cover boards. Its function is to protect the first or last leaves of the textblock. See also End Papers and Paste-down.

The Fore Edge is the edge of a leaf, textblock, or a board opposite from, and parallel to, its spine edge. Fore edge is also used in a more general way to refer to any part of a volume opposite from and parallel to its spine.

Foxing are spots or irregularly shaped stains that occur on paper. Foxing is caused either by fungi or iron impurities in paper, thought to be introduced during the paper's manufacture. Foxing may be controlled by maintaining relative humidity levels below 50%.

Gathering: see Signature

Grain Direction refers to the direction in which the majority of the fibers in a piece of paper or board are aligned and to the direction in which the warp threads run in cloth. Grain direction in all materials used in bookbinding should run parallel to the spine of a volume.

The Gutter of a volume is the groove and combined margin-space formed by the two inner or back margins of facing pages of a volume; closet to the spine.

The Head is the top edge of a leaf, board, or bound volume, opposite from the surface on which the volume rests when it is shelved upright. See also tail.

A Headband is a small ornamental band, generally of cotton or silk, which, in most modern publisher's trade bindings, is glued on the head as well as the tail of the textblock's spine. Modern headbands imitate the sewn-on headbands that functioned to protect the head and tail of early bindings.

The Headcap is the top edge of the cover's spine that runs parallel to the top headband. See also tailcap.

The Hinge is the flexible part of the cover on which the boards flex open. See also inner hinge and outer hinge.

To Hinge-In a leaf or a group of leaves a strip of Japanese tissue or linen tape is adhered along the binding edge of the leaf (or leaves) so that the strip extends beyond the binding edge. This can then be attached to the textblock by pasting up the part of the strip that extends beyond the leaf (or leaves), and adhering the strip to the binding edge of a leaf in the textblock.

A Hollow is that part or space of a case binding between the textblock spine and the inside of the cover spine.

An Inner Hinge is the groove lying between a paste-down and a flyleaf where the textblock is attached to its cover. Also called a front hinge and inner joint, this serves as the functional part of the book that allows the covers to be opened and closed.

Interleaving is the act of placing barrier sheets of acid-free or buffered paper between leaves or documents to prevent the transfer of media, acids, or damaging gases from one material to another.

Japanese Tissue is a soft, strong, long-fibered, and often translucent paper made from the fibers of a variety of plants common to Japan, especially the mulberry. It is available in a variety of thicknesses and colors. It is a very versatile paper, and according to the thickness used, it can be employed for mending torn paper, for overall lining of leaves as a reinforcement, for reinforcing the folds of signatures, for reinforcing fragile cloth spines, or for mending inner or outer hinges.

Kraft Paper is a strong brown machine-made paper widely used for wrapping purposes, and in publisher's bindings for lining the inside cover spine (spine strip) of a case-bound book.

A Leaf is a single sheet of paper or half of a folded sheet of paper.

Leaf Attachment is the structural method used to hold the pages of a volume together - creating a textblock. Some leaf attachment methods only employ dhesive to hold the pages together. Other methods employ thread that is used to sew together the pages of the text block.

Leather has been used as a book covering material for many centuries. There are many different methods by which animal hides are tanned or tawed to produce leather, resulting in a wide variety of strengths and aging properties.

Lignin is a component of woody plant fibers used to make most modern papers (not present in 100% cotton or linen paper). Its presence in paper contributes to chemical degradation of the paper.

The term Lignin Free refers to paper that contains no lignin. It may be 100% cotton or linen fibers or be chemically processed to remove the lignin from the wood pulp.

A Margin is the space around the edges of a page outside the printed or written matter. The four margins are commonly designated as: top margin; bottom margin; fore edge or outer margin; and inner or gutter margin.

Milling is a method used by library binders to remove old leaf attachments and prepare a text block for double-fan adhesive binding or oversewing. The milling machine clamps the textblock, spine down, and moves it over a series of rotating blades that cut away approximately 1/32 to 1/16 inch of the binding margin, thus removing old adhesive, thread, staples, and/or the folds of signatures. After milling, a text block is comprised of loose leaves.

Molds are microscopic fungal organisms that form masses on the surface of paper, book cloth, or leather. Molds can appear black, white or brightly colored and can range from dry and powdery to wet and slimy. Molds permanently deform the surfaces they inhabit.

A Mylar Laminate Cover is a covering material made by sandwiching the original paper cover from a paper-bound volume, or the dust jacket from a hard-bound volume, in between a laminate of polyethylene plastic and paper. This laminate is then used in the place of buckram to make the new cover. This product was developed to allow libraries to retain the original artwork or text found on paper-bound volumes or dust jackets.

Notching is a method for preparing the spine of a textblock for adhesive binding. The binder will cut very shallow, notches into the spine before applying the adhesive. These notches allow the adhesive to penetrate into the pages which greatly increases the strength of the leaf attachment.

The Outer Hinge is the flexible groove of covering material on the outside of a book on which the cover board opens. Also called the outer joint.

Oversewing is a long practiced leaf attachment method used to sew single leaves together. This leaf attachment method was very common in commercial binding, but has fallen out of favor in recent years except in specific cases. Individual leaves are grouped in small (1/8") gatherings that are side sewn together. The oversewing machine operator continuously feeds these small gatherings into the machine which sews the gatherings together. Oversewing can be recognized by its very inflexible spine and uneven, tight inner margin.

The Pastedown is the half of an endsheet that is glued to the inside of the cover board.

pH is a chemical measure of acidity or alkalinity obtained by measuring the quantity of free hydrogen ions in a solution. The pH scale is logarithmic (increases by multiples of 10) and runs from 0 to 14. A pH of 7.0 is neutral, while pH higher than 7.0 is alkaline and lower than 7.0 is acidic.

Permanent Paper is a paper that withstands the effects of aging better than ordinary paper. It is manufactured to resist chemical action from impurities in the paper or in the atmosphere during long term storage.

Pressure Sensitive Tape is any tape made of a film carrier with an active, pressure sensitive adhesive applied to one side. These tapes should not be used to repair torn leaves because the adhesives discolor and stain and are difficult or impossible to remove.

Protective Enclosures include boxes, slipcases, portfolios, or any other container that is designed to hold and protect books, manuscripts or other archival materials. Many commercial containers or custom-built protective enclosures are available for a variety of materials and needs.

Polyvinyl Acetate (PVA) is an emulsion adhesive that dries quickly and is considered permanent. It results in a very strong bond that remains flexible over time and does not yellow.

Rag Paper is paper made from cotton or linen fibers instead of wood pulp. Rag paper is stronger and more durable due to its chemical stability, low acidity, and long paper fibers.

Reversability pertains to the ability to undo a treatment or process without harming or changing the original object. Reversability is an important principle when performing conservation treatments on items with artifactual value.

Rounding is the process of hammering the textblock spine into a convex shape preparatory to backing. Rounding diminishes the effect of swelling caused by the thickness of the sewing threads or the application of glue from an adhesive binding. It also helps to prevent the textblock spine from falling into a concave shape after years of use or of standing upright on a shelf.

Section: see Signature

Sewn Through Fold refers to items with signatures sewn together. These items can be easily identified by looking for sewing thread in the inner margin of the middle of a signature.

The Shoulder is the outer edge of the textblock spine against which the cover board fits. The shoulder is made when a book is rounded and backed.

Signatures are two or more sheets of paper stacked and folded as a group. Also called a gathering, quire, or section. A textblock is made up of many gathered signatures sewn together.

Spine Linings are layers of cloth and paper used for reinforcing and stiffening the spine of the textblock. In many publisher's adhesive bindings, linings may not be used at all; the textblock is not reinforced and is held together simply with a layer of glue. Ideally, textblock spine linings should reinforce the glue and help hold the sections together.

Spine is the space between the boards of a case to accommodate the thickness of the textblock. The inside of this space is stiffened with a spine strip, usually made of bristol. A hinge area left on either side of the spine strip allows for the movement of the cover boards on the shoulders of the textblock as the book is opened and used. The outside part of the cover spine usually receives stamping for author, title, and publisher. This term may also be used to refer to the spine-edge of an uncased textblock.

The Square of the book is the exposed margin of the turn-in along the interior of the case not covered by the textblock or paste-downs. The square runs along the fore edge, top, and bottom edges of the book.

Stamping Foil is the lettering on the spine of a volume which is stamped into the book cloth using heat and pressure to transfer color (gold, white, or black) from a piece of carrier film to the cloth.

Stubbing is the process of adding sheets of paper to the textblock to accommodate pockets, inserts, or gaps.

Super is an open-weave variety of coarse, sized fabric used for reinforcing or stiffening the textblock spine of a case-bound book. The super forms the first spine lining on the textblock. The excess (super hinge) that extends beyond the edges of the textblock spine is used to attach the textblock into its case. Also called mull, crash, and gauze.

The Tail of a volume is the bottom portion of the cover and text block on which the book rests when it is on the shelf. See also head.

The Tailcap of a volume is the bottom portion of the spine. See also headcap.

The Text Block is the main block of gatherings or leaves, including endsheets and spine linings, which is bound together and then attached to the case. Also called the book block.

Tide Lines are irregular lines or blemishes caused by the movement of water or any other liquid through paper and the residual stains left behind as the liquid dries.

Tip-in, tipped-in, tipping-in is the attachment of one leaf to another in a book at or near the inner margin by means of a narrow strip of adhesive along the gutter edge of the sheet.

A turn-in is the part of the covering material that is turned over the outer edges of the boards (and spine strip) from the outside to the inside. Also called a turn-over or overlap.

Sources:

Jane Gammon. Conservation Information Sheet Number 1: Selected Glossary of Conservation and Preservation Terms