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Rabbit-skin glue is a sizing that also acts as an adhesive. It is a type of animal glue that is essentially refined rabbit collagen. The glue has been used for centuries for stretching and priming canvases for oil painting. It has also been an ingredient in traditional gesso.
In traditional oil painting as practiced by the Renaissance painter, skin glue was used to seal the canvas. This is necessary because the linseed oil that forms the base of most oil paint contains linolenic acid that will destroy the canvas fibers over time. Renaissance artists also knew that pure size (hide glue) became brittle once dry, and would mix it with oil and chalk to make a "half-ground" for canvases. Pure hide glue was usually applied only to rigid supports like panels. Though this does help to seal the canvas or panel, artists still applied a layer of "oil ground", which was often lead based paint, in order to provide a binding layer for the final oil paint to adhere to.
Rabbit skin glue is an animal glue created by prolonged boiling of animal connective tissue. Rabbit skin glue can be bought in powder form, little pellets or in larger chunks. Preparation involves using the correct proportion of water to glue to achieve the correct consistency and strength. It should be heated to just short of the boiling point. Too much heat results in a product with reduced adhesive qualities. Manufacturers of rabbit, and cow & horse hide glue recommend dissolving at 60–63 °C (140–145 °F).
As an adhesive, rabbit-skin glue is used in the production of the bellows of concertinas, and in other smaller, light instruments—prominently in violins. Its supreme advantages are very fast bonding and easy debonding with hot water, if an instrument must be disassembled for internal repairs. It also has very low creep, which is the tendency of some glues to plastically yield under even low but consistent stresses over time. For example, guitar bridges are subject to high lateral stresses that, with the wrong glue, can lead it to creep forward.
The proteins of the glue soak into the wood and interlace with its pores. Setting of the glue occurs with cooling and drying, so the working time is very short, on the order of minutes, to stick the parts together and get full strength, unlike PVA glue which might provide 20–30 minutes. Furthermore, since the glue only works by microscopically stitching the wood fibers together, any gaps in the joint are not going to be successfully filled, and so the mating surface must be very smooth.
When used in painting as a sizing, it is spread evenly over a canvas that has been placed on the stretcher. When the glue dries, it tightens the canvas. The canvas should be left to dry in normal room temperature for at least 12 hours. Under no circumstances should the canvas be placed to dry under harsh sunlight or other heat, because the glue will start to crack. Air humidity also affects how tight the canvas will dry. This process should be then repeated once more. After this if needed, the canvas can be lightly sanded flat. [1] Then an oil-based primer is applied.
A canvas sized with rabbit-skin glue can be made tighter than with other alternatives—such as an acrylic-based gesso—because of the shrinkage. This type of canvas is also valuable because it can be sanded to a flatter texture, which allows the painter to achieve a finer level of detail than can be achieved with a typical acrylic gesso ground.
This rabbit-skin glue ground is only appropriate for use under oil paint. Acrylic-based media will flake off a canvas prepared with rabbit-skin glue and are therefore not appropriate. [2]
Rabbit skin glue is considered to be a major cause of cracking in oil paintings by most modern conservators. Because the glue is hygroscopic, it continually absorbs moisture from the atmosphere, causing the glue to swell and shrink as ambient humidity levels change. Over many humidity cycles, this repeated flexing causes the brittle oil paint to crack. Modern substitutes for rabbit skin glue are available, such as Gamblin's PVA size [3] and Golden Acrylics’ GAC100. These substitutes do not have the hygroscopic properties of rabbit skin glue, while still being very slightly hygroscopic, and should not cause the damage to oil paints that rabbit skin glue does. However, these modern replacements do not stiffen and tighten the canvas as well as rabbit skin glue does, so some artists still prefer to use rabbit skin glue.
Acrylic paint is a fast-drying paint made of pigment suspended in acrylic polymer emulsion and plasticizers, silicone oils, defoamers, stabilizers, or metal soaps. Most acrylic paints are water-based, but become water-resistant when dry. Depending on how much the paint is diluted with water, or modified with acrylic gels, mediums, or pastes, the finished acrylic painting can resemble a watercolor, a gouache, or an oil painting, or have its own unique characteristics not attainable with other media and are meant for canvases.
Oil painting is a painting method involving the procedure of painting with pigments with a medium of drying oil as the binder. It has been the most common technique for artistic painting on canvas, wood panel or copper for several centuries, spreading from Europe to the rest of the world. The advantages of oil for painting images include "greater flexibility, richer and denser colour, the use of layers, and a wider range from light to dark". But the process is slower, especially when one layer of paint needs to be allowed to dry before another is applied.
Gesso, also known as "glue gesso" or "Italian gesso", is a white paint mixture used to coat rigid surfaces such as wooden painting panels or masonite as a permanent absorbent primer substrate for painting. It consists of a binder mixed with chalk, gypsum, pigment, or any combination of these.
Gouache, body color, or opaque watercolor is a water-medium paint consisting of natural pigment, water, a binding agent, and sometimes additional inert material. Gouache is designed to be opaque. Gouache has a long history, having been used for at least twelve centuries. It is used most consistently by commercial artists for posters, illustrations, comics, and other design work.
Canvas is an extremely durable plain-woven fabric used for making sails, tents, marquees, backpacks, shelters, as a support for oil painting and for other items for which sturdiness is required, as well as in such fashion objects as handbags, electronic device cases, and shoes. It is popularly used by artists as a painting surface, typically stretched across a wooden frame.
Sizing or size is a substance that is applied to, or incorporated into, other materials—especially papers and textiles—to act as a protective filler or glaze. Sizing is used in papermaking and textile manufacturing to change the absorption and wear characteristics of those materials.
Craquelure is a fine pattern of dense cracking formed on the surface of materials. It can be a result of drying, shock, aging, intentional patterning, or a combination of all four. The term is most often used to refer to tempera or oil paintings, but it can also develop in old ivory carvings or painted miniatures on an ivory backing. Recently, analysis of craquelure has been proposed as a way to authenticate art.
Marouflage is a technique for affixing a painted canvas to a wall, using an adhesive that hardens as it dries, such as plaster or cement.
Animal glue is an adhesive that is created by prolonged boiling of animal connective tissue in a process called rendering. In addition to being used as an adhesive it is used for coating and sizing, in decorative composition ornaments, and as a clarifying agent.
Wood glue is an adhesive used to tightly bond pieces of wood together. Many substances have been used as glues. Traditionally animal proteins like casein from milk or collagen from animal hides and bones were boiled down to make early glues. They worked by solidifying as they dried. Later, glues were made from plant starches like flour or potato starch. When combined with water and heated, the starch gelatinizes and forms a sticky paste as it dries. Plant-based glues were common for books and paper products, though they can break down more easily over time compared to animal-based glues. Examples of modern wood glues include polyvinyl acetate (PVA) and epoxy resins. Some resins used in producing composite wood products may contain formaldehyde. As of 2021, “the wood panel industry uses almost 95% of synthetic petroleum-derived thermosetting adhesives, mainly based on urea, phenol, and melamine, among others”.
Aging is a process by which an artwork, typically a painting or sculpture, is made to appear old. It is meant to emulate the natural deterioration that can occur over many decades or centuries. Although there may be "innocent" reasons for it, ageing is a technique very often used in art forgery.
Acrylic painting techniques are different styles of manipulating and working with polymer-based acrylic paints. Acrylics differ from oil paints in that they have shorter drying times and are soluble in water. These types of paint eliminate the need for turpentine and gesso, and can be applied directly onto canvas. Aside from painting with concentrated color paints, acrylics can also be watered down to a consistency that can be poured or used for glazes.
Glue-size is a painting technique in which pigment is bound (sized) to cloth with hide glue, and typically the unvarnished cloth was then fixed to the frame using the same glue. Glue-size is also known as distemper, though the term "distemper" is applied variously to different techniques. Glue-size was used because hide glue was a popular binding medium in the 15th century, particularly among artists of the Early Netherlandish period, who used it as an inexpensive alternative to oil. Although a large number of works using this medium were produced, few survive today, mainly because of the high perishability of linen cloth and the solubility of hide glue. Well-known and relatively well-preserved – though substantially damaged – the most notable examples include Quentin Matsys' Virgin and Child with Saints Barbara and Catherine and Dirk Bouts' Entombment. In German the technique is known as Tüchleinfarben, meaning "small cloth colours", or Tüchlein, derived from the German word for “handkerchief”.
Conservation and restoration of ceramic objects is a process dedicated to the preservation and protection of objects of historical and personal value made from ceramic. Typically, this activity of conservation-restoration is undertaken by a conservator-restorer, especially when dealing with an object of cultural heritage. Ceramics are created from a production of coatings of inorganic, nonmetallic materials using heating and cooling to create a glaze. These coatings are often permanent and sustainable for utilitarian and decorative purposes. The cleaning, handling, storage, and in general treatment of ceramics is consistent with that of glass because they are made of similar oxygen-rich components, such as silicates. In conservation ceramics are broken down into three groups: unfired clay, earthenware or terracotta, and stoneware and porcelain.
The lining of paintings is a process of conservation science and art restoration used to strengthen, flatten or consolidate oil or tempera paintings on canvas by attaching a new support to the back of the existing one. The process is sometimes referred to as relining. Most often a new support will be added directly to the back of an existing canvas. In cases of extreme decay, however, the original canvas may be completely removed and replaced. The height of the practice's use peaked in the late 19th century and in the following years its usefulness has been debated. There are many different factors that influence whether lining a painting will be successful. By paying close attention to an artwork's condition and response to treatment, conservation professionals better understand the lining process and when to apply it.
The conservation and restoration of painting frames is the process through which picture frames are preserved. Frame conservation and restoration includes general cleaning of the frame, as well as in depth processes such as replacing damaged ornamentation, gilding, and toning.
The conservation and restoration of paintings is carried out by professional painting conservators. Paintings cover a wide range of various mediums, materials, and their supports. Painting types include fine art to decorative and functional objects spanning from acrylics, frescoes, and oil paint on various surfaces, egg tempera on panels and canvas, lacquer painting, water color and more. Knowing the materials of any given painting and its support allows for the proper restoration and conservation practices. All components of a painting will react to its environment differently, and impact the artwork as a whole. These material components along with collections care will determine the longevity of a painting. The first steps to conservation and restoration is preventive conservation followed by active restoration with the artist's intent in mind.
The conservation-restoration of panel paintings involves preventive and treatment measures taken by paintings conservators to slow deterioration, preserve, and repair damage. Panel paintings consist of a wood support, a ground, and an image layer. They are typically constructed of two or more panels joined together by crossbeam braces which can separate due to age and material instability caused by fluctuations in relative humidity and temperature. These factors compromise structural integrity and can lead to warping and paint flaking. Because wood is particularly susceptible to pest damage, an IPM plan and regulation of the conditions in storage and display are essential. Past treatments that have fallen out of favor because they can cause permanent damage include transfer of the painting onto a new support, planing, and heavy cradling. Today's conservators often have to remediate damage from previous restoration efforts. Modern conservation-restoration techniques favor minimal intervention that accommodates wood's natural tendency to react to environmental changes. Treatments may include applying flexible battens to minimize deformation or simply leaving distortions alone, instead focusing on preventive care to preserve the artwork in its original state.
In visual arts, the ground is a prepared surface that covers the support of the picture and underlies the actual painting. Occasionally the term is also used in a broad sense to designate any surface used for painting, for example, paper for watercolor or plaster for fresco.