Animal glues — hide glue and fish glue — are the oldest wood glues still in use. They have bonded everything from Egyptian furniture in Tutankhamun's tomb to Stradivarius violins and 18th-century French commodes. Their unique property is reversibility: a joint can be dissolved again with heat and moisture without damaging the wood. That makes them indispensable for furniture restoration, antiques work, instrument building and the conservation of cultural heritage objects. This guide covers the chemistry, history, traditional and modern application, the difference between hide glue and fish glue, as well as when to choose animal glue over modern PVA.
If you just want a quick recommendation: for restoring an antique piece of furniture or repairing a stringed instrument joint — use Titebond Liquid Hide Glue or classic granules. If you want to understand why — read on.
3,000 years of animal glues — a brief history
Animal glues are the first wood glue humanity produced. Archaeologists have found hide glue residues on Egyptian furniture dated to 3400 BC — including wooden artefacts in Tutankhamun's tomb (c. 1323 BC) where the joints still hold more than 3,300 years later [1]. The first written recipes come from Mesopotamia and Egypt: hides and sinews from cattle and horses were boiled down into a gelatine mass that was dried and stored in blocks or pearls.
In Europe, hide glue became the standard glue for furniture making during antiquity and continued to dominate until the middle of the 20th century. The Stradivarius violins from Cremona (1660-1737) are hide-glued in every joint — including the joining of the top with the rib, and the attachment of the neck [2]. Antonio Stradivari chose hide glue not only because it was the only option but for an acoustic property: hide glue joints transmit vibrations better than modern elastic glues, which influences the instrument's tone.
The furniture factories of Paris, London and New York used hide glue exclusively until the 1930s, when the first synthetic glues began to compete. Chippendale, Hepplewhite, Thomas Sheraton — all were built with hide glue. That is why we must use the same material today when restoring them: only hide glue bonds to an existing hide glue joint without requiring you to break away 300-year-old patina.
Franklin International, the maker of Titebond, was founded in 1935 with liquid hide glue as its first product [3]. During the Second World War, casein glues and early PVA glues then replaced hide glue in industry, but the restoration world has never left the animal-glue heritage behind.
Hide glue — chemistry and manufacture
Hide glue is not a specific recipe but a family of collagen-based glues where the raw material determines the quality. The basic process is the same:
- Raw material: Hides, sinews, bones and cartilage from mammals — in Sweden most often cattle, historically also horse.
- Liming: The raw material is treated with a lime solution to dissolve hair, fat and organic material.
- Extraction: The material is boiled in water at 60-90°C for several hours. The collagen in the hide denatures and is converted into gelatine, which dissolves in the hot water.
- Filtering and concentration: The liquid is strained and concentrated by evaporation.
- Drying: The thick gelatine solution is cast in a thin film, dried and then broken into granules, pearls or sheet flakes.
Finished hide glue is graded by gel strength (Bloom grams) — a measure of the firmness of the gelatine. For furniture making, 192 gram Bloom strength is commonly used; for fine restoration a lower gram strength is used, giving a longer open time and less shrinkage.
How hide glue works chemically
When the granules are soaked, the collagen chains swell and absorb water. On heating to 55-65°C, the chains separate completely and form a liquid solution. Applied to the timber surface, bonding occurs through two mechanisms:
- Mechanical infiltration — the solution penetrates the pores and lumen structures of the wood before gelling.
- Hydrogen bonding — as the glue dries, the gelatine forms hydrogen bonds with the cellulose in the wood, giving the joint its strength.
Unlike PVA, which sets through water evaporation and chemical polymerisation, hide glue gels first (on cooling below 35°C) and then cures through loss of water. It is this two-stage process that makes hide glue reversible — heat restores the gel phase without breaking down the collagen.
Fish glue — isinglass and its particular properties
Fish glue, known internationally as isinglass, is a collagen glue made from fish material — traditionally dried swim bladders from sturgeon (beluga, sevruga, Russian sturgeon) [4]. Today other species such as burbot, cod and catfish are also used, but the historically highest quality came from the Russian Caspian Sea.
Differences compared with hide glue
Fish glue collagen differs from mammalian collagen at the molecular level:
- Lower gelling temperature — fish glue only gels at around 8-15°C compared with hide glue's 25-30°C, giving a longer open time at room temperature.
- Higher purity — fish glue is almost completely transparent and the joint is practically invisible on light-coloured timbers.
- More flexible joint after curing, which makes it better for thin veneers that move with moisture changes.
- Considerably more expensive — pure sturgeon-bladder isinglass can cost 10-20 times more than hide glue per litre of ready solution.
Traditional uses
Fish glue has historically been used where hide glue was too stiff or too visible:
- Gilding — attaching gold and silver leaf to wood and gesso (gesso technique).
- Parchment and book restoration — still used by archive conservators.
- Thin veneering on furniture — particularly light-coloured French 18th-century furniture.
- Stringed instruments — primarily for re-gluing loose tops where fish glue can penetrate into fine cracks that hide glue is too thick for.
- Wine clarification — fish glue has historically been used in brewing as a fining agent.
Why animal glues in restoration — the ethics of reversibility
The single most important property of hide glue and fish glue is that the joint is reversible: it can be heated with steam or a damp cloth to 60°C, whereupon the glue returns to gel form and can be released with gentle pressure. The surface does not need to be sanded, scraped or otherwise damaged.
This is an ethical principle within museum conservation: everything done to a historical object should be reversible as far as possible. If someone in 100 years' time is to treat the piece of furniture again — perhaps with new techniques we don't know today — today's intervention must not block that possibility. International standards such as the ICOM-CC Code of Ethics and the AIC Code of Ethics and Guidelines for Practice formulate this as a fundamental professional ethical principle [5].
What happens if you glue an antique piece of furniture with Titebond III?
Technically: the joint becomes stronger than the wood. But:
- The next restorer cannot release the joint without breaking the wood around the glue.
- The modern glue joint often shows as a darker line as the piece ages — hide glue joints become invisible after decades.
- The value of the piece falls for collectors — a Chippendale chair re-glued with modern PVA is considered "ruined" from an antiques point of view.
- If the wood cracks again you cannot melt-glue the joint in place; the whole section must be sanded away and replaced.
Therefore the rule: for anything pre-1940, and for anything that has or may have collector or museum value — use hide glue or fish glue.
<CallOut type="info" title="Is your piece of furniture "old enough"?"> Rule of thumb: If the piece is from before the 1940s or if you do not know with certainty that it was built with modern glues, re-glue it with hide glue. For an IKEA piece from the 1980s, Titebond II or III is enough. Unsure? Take a small piece from an existing joint and put it in hot water — if it dissolves in 10-15 minutes it is animal glue, and it should be re-glued with the same.
Granules and pearls vs liquid hide glue
Hide glue has historically been sold in three forms: granules, pearls (pellets) and flat flakes. All are the same product — just different drying and crushing forms. Granules dissolve fastest (30-60 min soaking), flakes the slowest (up to 12 hours). Pearls are the most common in the European trade today.
Titebond Liquid Hide Glue — the modern alternative
Franklin's liquid hide glue is a more significant invention than many realise. Traditional hide glue gels as soon as it cools below 30°C — which means you have about 30-60 seconds to apply glue to both surfaces, assemble and clamp. For a restorer who glues daily it is a matter of habit; for a hobby user who glues a chair once a year it is almost impossible.
Titebond Liquid Hide Glue solves this by adding urea (carbamide) to the formulation [6]. The urea keeps the collagen in solution at room temperature — the bottle stands in the workshop and you apply directly without a double boiler. Open time is around 10 minutes at 20°C, which is twice as long as both ordinary PVA and traditional hot hide glue.
Franklin's liquid hide glue retains reversibility — the joint can still be dissolved with heat and moisture, which makes it a legitimate restoration product. It is however not approved for museum conservation of objects in the highest value class, because the urea addition does not match the chemistry of 18th-century original joints exactly. For an everyday restoration of a grandmother's chair, the family piano or an antique chest of drawers at home — an excellent choice.
Traditional mixing and heating — step by step
If you are restoring a piece of furniture of the highest class or building a stringed instrument, liquid hide glue is not enough. Here is the traditional process:
1. Soaking
Weigh out granules and cold water in the ratio 1:1.5 to 1:2 by weight — more water for thinner glue (fish-glue consistency), less for stronger (furniture joint). Mix in a heat-resistant container — glass or stainless steel, never aluminium, which reacts with collagen.
Leave to stand for:
- 30-60 min for fine granules
- 2-4 hours for pearls
- 8-12 hours for flakes
The glue has drawn up all the water and formed a thick jelly when it is ready.
2. Heating (double boiler / bain-marie)
Place the soaked container in a larger saucepan with water. Heat the water bath to 60-65°C — use a thermometer. NEVER use direct heat: boiling point destroys the collagen permanently [7].
Stir slowly until all granules have melted and the solution is homogeneous (5-15 min). The consistency should resemble thick cream — it runs off the brush but does not drip.
3. Application
Use a short, stiff brush with natural bristles. Apply a thin coat to both surfaces. Important with hide glue: the surfaces should be pre-warmed — a cold surface gels the glue immediately on contact and prevents penetration. Use a heat lamp, a hair dryer or pre-warm the parts on a warm-air radiator.
Assemble and clamp within 30-60 seconds after application. Yes, that is quick. That is why restorers practise gluing on scrap pieces before they touch the original.
4. Clamping pressure and clamping time
- Clamping pressure: 0.5-1.0 MPa — about the same as for PVA.
- Minimum clamping time: 15 minutes at 20°C (the glue has gelled and the joint can be handled).
- Full cure time: 24 hours at 20°C and 50 per cent RH — the joint reaches full strength once the residual water has diffused out.
Hide glue wets wood very well thanks to its water solubility — better than most PVAs. That means you can often get by with lower clamping pressure than with Titebond, which is important for thin antique elements where high load can crack the wood.
Durability and limitations
Hide glue and fish glue joints are exceptionally durable under the right conditions:
Strengths:
- Lifespan: 300+ years documented on Stradivarius violins and 17th-century furniture.
- Joint strength in dry condition: 70-90 kg/cm² — on a par with PVA.
- Ages beautifully: becomes transparent and invisible when it dries fully, unlike PVA which yellows.
- Sounds good — does not affect the wood's resonance properties, important for instruments.
Weaknesses:
- Moisture: humidity above 70 per cent RH for extended periods softens the glue and the joint can creep.
- Water: direct water contact makes the joint unusable within 30-60 minutes.
- Heat: above 50°C the joint starts to soften, above 60°C it releases completely.
- Cold + damp: repeated freeze cycles with water destroy the joint.
- Mould: animal protein can go mouldy at high humidity; traditional recipes sometimes contain small amounts of preservative (salicylic acid, thymol).
Applications where hide glue does NOT suit:
- Outdoors (regardless of cover)
- Kitchen, bathroom, utility room (high humidity)
- Boats, caravans, any mobile vehicle
- Cutting boards, dining tables with heavy water spills
- Floors and stairs with high mechanical load
Use cases — where hide glue and fish glue shine
Restoration of antique furniture
A Chippendale chair from 1780 will certainly have several loose hide-glue joints. The solution: steam an existing joint, release carefully, clean old glue from both surfaces with warm water and a soft brush, apply new hide glue and clamp. Because new hide glue bonds to old hide glue chemically, you get a joint as strong as the original — without having to sand away the original surface.
Veneering
18th-century French furniture (Louis XV, Louis XVI) is veneered with thinly sawn sheets of exotic timbers — walnut, mahogany, satinwood. The veneering was traditionally lifted off with a warm iron and the hide glue was reactivated. For period-true restoration: lay new veneer with hide glue, iron with a warm iron (75-85°C through damp cloth) and the glue penetrates perfectly without lumps. This is impossible with modern PVA contact adhesive.
Stringed instruments
Violins, violas, cellos, acoustic guitars, lutes, mandolins — all are built traditionally with hide glue. Reversibility is decisive: a violin maker must be able to release the top to adjust supports, change bass bars or repair cracks without damaging the precious resonance wood. Hide glue is also acoustically neutral — it does not dampen vibrations the way elastic glues do.
Gilding
Gold leaf is traditionally fixed in a hide or fish glue solution (gesso sottile) prepared with chalk and fish glue. Pure fish-glue isinglass gives the sharpest, most transparent glue line that is not visible under the paper-thin gold.
Conservation of museum objects
ICOM-CC and conservation laboratories across the world use hide glue and fish glue in their standard work on wood, paper, parchment and leather materials. The argument is always the same: reversibility and compatibility with historical materials.
Hide glue vs fish glue vs PVA vs polyurethane — when do you choose what?
<CompareTable caption="Animal glues compared with modern wood glues" columns={[ { key: "lim", label: "Glue", highlight: true }, { key: "reversibel", label: "Reversible" }, { key: "utomhus", label: "Outdoors" }, { key: "oppen", label: "Open time" }, { key: "primar", label: "Primary use" } ]} rows={[ { lim: "Traditional hide glue (granules)", reversibel: "Yes (heat + moisture)", utomhus: "No", oppen: "30-60 sec", primar: "Antique restoration, instruments, museum conservation" }, { lim: "Titebond Liquid Hide Glue", reversibel: "Yes (heat + moisture)", utomhus: "No", oppen: "10 min", primar: "Everyday restoration, family antiques, repairs" }, { lim: "Fish glue (isinglass)", reversibel: "Yes (heat + moisture)", utomhus: "No", oppen: "5-10 min", primar: "Gilding, parchment, thin veneering, fine finish" }, { lim: "Titebond Original PVA (D2)", reversibel: "No", utomhus: "No", oppen: "5 min", primar: "Ordinary indoor furniture, shelves, drawers" }, { lim: "Titebond III PVA (D4)", reversibel: "No", utomhus: "Yes", oppen: "8-10 min", primar: "Outdoor furniture, cutting boards, boat interior" }, { lim: "Polyurethane (PU, D4)", reversibel: "No", utomhus: "Yes", oppen: "30 min", primar: "Metal-to-wood, moisture-activated, mixed materials" } ]} />
The decision tree:
- Antique furniture (before around 1940) or stringed instrument? → Hide glue (granules or liquid)
- Gilding, veneering, conservation? → Fish glue
- Modern indoor furniture? → Titebond Original (D2) or II Premium (D3)
- Outdoors, food contact, boat? → Titebond III Ultimate (D4)
- Metal-to-wood or mixed materials? → Titebond Polyurethane
See also our complete guide to the Titebond range for modern PVA choices.
Hide glue — practical tips from the workshop
After many years of restoration work, Ernst P's workshop has gathered practical lessons:
- Buy fresh. Hide glue granules keep 2-3 years dry and cool. Older granules take longer to dissolve and give a weaker joint. Check the best-before date.
- Mix only what you will use the same day. Ready-mixed hide glue gels and moulds after 3-5 days in the fridge. Kept warm, 8 hours maximum.
- Pre-warm everything. Wood, clamps, cauls — anything that touches the glue should be 25-30°C. Cold surfaces kill the joint.
- Keep a glue log. Record temperature, humidity, water/granule ratio and result. After 10 glue-ups you will see patterns.
- Practise on scrap first. Hide glue is time-critical. Keep a scrap piece to one side and practise application + assembly three times before you go on the original.
- Clean the brush in hot water, never solvent. Gelatine is water-soluble.
- If a joint didn't take — don't panic. Steam the surface, scrape the old glue off carefully, re-glue. This is hide glue's great advantage.
Sources
All technical values and historical facts in this guide are verified against the primary sources below. Last updated 2026-04-18.
- Getty Conservation Institute — "The Structural Conservation of Panel Paintings". Historical overview of animal glues in wooden artefacts including Egyptian finds. getty.edu/publications
- The Strad — "The Adhesives Used in Violin Making". Technical review of hide glue in Stradivarius and modern luthier tradition. thestrad.com
- Franklin International — A History of Excellence. Franklin's official company history confirms the 1935 founding with liquid hide glue as the first product. franklinap.com/blog/a-history-of-excellence
- Conservation Wiki (AIC) — Isinglass. American Institute for Conservation — description of fish glue from sturgeon bladders, history and use in conservation. wiki.culturalheritage.org
- ICOM-CC Code of Ethics for Museums. International Council of Museums — ethical guidelines on reversibility in conservation work. icom.museum
- Titebond Liquid Hide Glue — Technical Data Sheet. Franklin TDS: open time 10 min, clamp time 24 h, urea addition for liquid consistency, reversible with heat + moisture. titebond.com
- Popular Woodworking — "Hide Glue: Historical & Practical Substance". Technical article on hide glue temperature sensitivity, Bloom strengths and traditional preparation. popularwoodworking.com
- Smithsonian Museum Conservation Institute — "Animal Glues". Smithsonian MCI overview article on hide glue and fish glue in cultural heritage conservation. si.edu/mci
Vanliga frågor
What is hide glue?
Hide glue is an animal glue made from collagen extracted from animal hides, sinews and bones — traditionally from cattle. The collagen is boiled down to gelatine, dried into granules or pearls, and then dissolved in water and heated to roughly 60°C before application. Hide glue has been used in furniture making for more than 3,000 years and remains the gold standard for the restoration of antique furniture, violins and other stringed instruments thanks to its reversibility.
What is the difference between hide glue and fish glue?
Both are collagen-based animal glues, but the raw material differs. Hide glue comes from mammalian hides and sinews (most often cattle). Fish glue (isinglass) comes traditionally from the dried swim bladders of sturgeon and other fish. Fish glue has higher purity, gives a more flexible and nearly invisible joint, and has a lower gelling temperature — but it is also considerably more expensive. Hide glue is stronger on wider joints; fish glue is preferred for gilding, conservation and thin veneering.
Why are animal glues used in furniture restoration?
Reversibility. A hide glue or fish glue joint can be dissolved again with heat (about 60°C) and moisture without damaging the wood or the original patina. This means an antique piece of furniture can be dismantled, repaired and re-glued by the next generation's restorer — without having to break apart the original joints. Modern PVA glues (Titebond, Gjöco) and epoxy are practically impossible to reverse, which makes them unsuitable for museum objects and antiques.
How is traditional hide glue mixed and heated?
Soak granules or pearls in cold water for 30 minutes to 12 hours (depending on the gram strength) until they have swelled into a jelly. Then heat in a double boiler (bain-marie) to 55-65°C — never above 65°C, as the collagen breaks down and the glue loses strength. The glue should have the consistency of thick cream. Use it immediately and hot; it gels within minutes at room temperature. A common mix ratio is 1 part granules to 1.5-2 parts water by weight.
How long does a hide glue joint last?
Done properly in a dry indoor environment: hundreds of years. Stradivarius violins from the 1700s are still held together by their original hide glue joints. Hide glue is however not water-resistant and does not tolerate sustained humidity above 70 per cent, which is one of the reasons it is not used for outdoor projects or kitchen and bathroom environments.
Can I use Titebond Liquid Hide Glue instead of traditional granules?
Yes, for most restoration jobs. Franklin/Titebond's liquid hide glue contains the same collagen base with additions of urea that keep the glue liquid at room temperature — no double boiler is needed. It is reversible, gives the same characteristic joint strength and is an excellent modern alternative for restorers who don't glue every day. For conservation of museum objects with the highest demands for authenticity, traditional granulated hide glue that can be matched exactly to the original joint is however still used.
