Hoof glue is an adhesive

Adhesive

An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...

 made by boiling down the hooves

Hoof

A hoof , plural hooves or hoofs , is the tip of a toe of an ungulate mammal, strengthened by a thick horny covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick nail rolled around the tip of the toe. The weight of the animal is normally borne by both the sole...

 of ungulate

Ungulate

Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...

s. It is a partially hydrolyzed

Hydrolysis

Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 keratin

Keratin

Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...

. It is a type of animal glue

Animal glue

An animal glue is an adhesive that is created by prolonged boiling of animal connective tissue.These protein colloid glues are formed through hydrolysis of the collagen from skins, bones, tendons, and other tissues, similar to gelatin. The word "collagen" itself derives from Greek κόλλα kolla, glue...

.

History

Hoof glue was widely used throughout human history. The oldest known bow

Bow (weapon)

The bow and arrow is a projectile weapon system that predates recorded history and is common to most cultures.-Description:A bow is a flexible arc that shoots aerodynamic projectiles by means of elastic energy. Essentially, the bow is a form of spring powered by a string or cord...

 is 9780 years old and made using hoof glue. Hoof glues have been used for things like stiffening bow strings, adhering fabric to wood, stiffening fabric, creating thin lacquers to protect valuable objects , as well as sealing glass into frames, and sealing ceramic containers to name just a few. Hoof glue is still used today in cabinet

Cabinet making

Cabinet making is the practice of using various woodworking skills to create cabinets, shelving and furniture.Cabinet making involves techniques such as creating appropriate joints, dados, bevels, chamfers and shelving systems, the use of finishing tools such as routers to create decorative...

ry and other fine woodworking projects where the joints must be extremely fine if not invisible.

Formulation

The general process is to take the hooves of ungulates and break them into small chunks and then boil them in water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 until all the hoof material has been liquefied. An acid

Acid

An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

 is then added to create a thick gel

Gel

A gel is a solid, jelly-like material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state...

. The resultant product is then cooled and allowed to harden.

Usage

The storable form of hoof glue is a hard block of resin

Resin

Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...

-like material. To use it one would break off a suitably sized chunk and mix it with hot water and allow it to melt. Once melted it can be simmered

Simmering

Simmering is a food preparation technique in which foods are cooked in hot liquids kept at or just below the boiling point of water , but higher than poaching temperature...

 to reduce to the appropriate thickness and then applied to the object in question. Very thin glue can be used as a resin coating to stiffen and strengthen cordage, such as bow strings or chair backs and seats. Hoof glue is not waterproof

Waterproofing

Waterproof or water-resistant describes objects relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environments or under water to specified depths...

. Hoof glue does not become brittle when dry; it retains some flexibility, thus making it ideal for applications where some give in the joint or covering is required.