The use of hide glue

Bone glue has been a common carpenter's glue for centuries and is made from bones. The glue brews are cleaned, evaporated, and dried, resulting in a solid jelly form. Bone glue is completely harmless and environmentally friendly.

There is no piece of furniture from the 19th century that is not assembled with this glue. Even until the mid-20th century, bone glue was the predominantly used glue in furniture construction. However, for industrial production methods, the properties of this glue were rather hindering, as it had to be made usable by dissolving it in water and heating it. Due to the prefabrication processing in many areas of craftsmanship, it has also been largely pushed back there and is now almost only used in the field of restoration.

A mistake, we think. Anyone seriously engaged in furniture construction and its fundamentals should also explore these fundamentals, as a glue that has been used for centuries must have its benefits. One gains a new feeling for the material and its work, and sharpens one's eye for the details. Many who have switched from white glue to bone glue stick with it and particularly appreciate the properties that correspond to the organic material wood.

There are some compelling arguments in favor of bone glue:

• It is reversible, meaning that a glued joint can later be undone using heat. This is still possible even after 100 years.
• Repairs and rectifying mistakes - everyone can make a mistake - can be easily accomplished compared to commercial white glues. Warm the workpiece slightly, loosen as necessary, possibly add some moisture, and re-glue, and the mistakes are corrected.
• The pearls are practically indefinitely durable in dry condition. Even mixed glues that have dried out over the years are usually fully usable again after adding water and heat.
• The glue dries hard and firm and does not form a plastic skin on the wood like white glue. As an organic product, it fits better with wood than plastic.
• It is environmentally friendly and can be used without danger. I once knew a carpenter who enjoyed slurping it. However, I do not recommend it.

Instructions for use

Take a normal drinking glass and pour the glue pearls into it. Maximum up to half of the glass! Then pour in water up to the height of the top edge of the filled glue pearls. Let it soak overnight!

Then heat a pot of water over a stove and place the container with the soaked glue inside, stirring occasionally with a wooden stick. After just a few minutes, you will have a ready-to-use glue that can still be diluted further with water. Do some experiments, and soon you will have the glue consistency that is most suitable for your work. The glue should not boil. If it boils, it can become unusable, but in my experience, it does not necessarily have to.

To apply the glue, you can use a brush (the ferrule that holds the bristles together should not be made of iron) or - which has also proven very effective for small areas - small veneer pieces (but not made of oak, as its tannic acid reacts with the glue - you can still glue oak with this glue). The further procedure depends on what you are gluing.

If you are veneering a piece of wood: The substrate should be warmed for veneering. The substrate is a piece of solid material: aluminum plates, galvanized iron plates, wood blocks, which serve to ensure that the veneer is pressed smoothly and cleanly between the blind wood (wood to which the veneer is glued) and the clamp. Bone glue gels relatively quickly after application. This means that upon cooling, it takes on a jelly-like consistency, and proper pressing is no longer possible because it has become too viscous and thick. Therefore, carpenters in ancient times worked very quickly when gluing. However, we do not have to put ourselves through that. The hot substrate ensures that the glue becomes soft again, and we can calmly apply the clamps. When tightening the clamps, the so-called "glue cord" forms at the outer edges, a sure sign that it is gluing well.

If you are gluing wood together: For example, when applying glue to a mortise joint, only a very short time should pass before joining and tightening the clamps. The aforementioned gelling prevents a clean joining. You can easily avoid this by warming the pieces to be glued, allowing you to proceed with the necessary care and as slowly as your practice allows.

Setting time: Generally, the clamps can be removed after 10 to 20 minutes. However, the workpiece should rest for another day before further work is done. Make sure that it is not too cold in the workshop. Room temperature is good; I would leave the work if it is below 15 °C.

Dealing with oozing glue: Of course, you can wait until everything is completely dry and then remove the excess glue. The danger here is that the glue has bonded so firmly with the wood that you will need a very sharp tool and some practice to remove the glue without damaging the workpiece. Despite the rule that a workpiece should rest for another day after gluing, I recommend doing this work immediately. As long as the glue is still soft, it can be easily removed with an old chisel (used like a scraper) or a pull knife. In individual cases, moisten the surface slightly at the spot.

Storage: To avoid having to store too much, do not mix more than the daily requirement. The requirement for the next day is easily made: add some grains and the corresponding amount of water to the glue pot with the leftover glue and let it swell overnight; the next morning, proceed as described above. An extra pot is not necessary. When your project is finished and you do not need glue in the foreseeable future: leave the pot open and let it dry out! A lid only promotes mold growth! If you are lucky, the glue dries out before mold forms, and it can be regenerated with water. If you are unlucky, mold forms, then throw the rest away.

Additional remarks:

Instead of a drinking glass, you can use all sorts of other containers: ceramic, enamel, aluminum, or any other heat-resistant pot that is not made of iron. Iron turns the glue black and makes it unusable! With a normal drinking glass, be careful not to heat it too much; it could break. Use a heat-resistant laboratory glass if you have one available.

When gluing with substrates, always use a separating layer of paper. If you forget this, you may end up gluing the substrate as well. The remaining paper residues after removing the substrate can be easily re-moistened and removed with an old chisel.

What devices are suitable for heating glue, substrates, and wood?

There are no limits to imagination. In the past, there were glue ovens in carpentry shops that were 2 square meters in size and heated by the shavings generated in the workshop. On it, both all workpieces and the glue pot had their place. Depending on how often you want to approach such a thing, there are various expensive or cheap ways. The simplest way is an old hot plate that might otherwise just be sitting around. However, caution: even at the "1" setting, the plate can be so hot that placed wood chars or burns. Fire hazard! The water bath on these plates is, however, not a problem. Then there are warming plates from the restaurant sector, which I have not yet tried myself, but some users swear by them. The best are heating plates used for modern veneer systems, which can be obtained from the manufacturer in any desired size. They allow for fine temperature regulation and can even be used as a substrate. However, these are expensive. When purchasing, choose a heating option large enough so that not only the glue pot but also substrates and possibly parts of the workpiece can fit on it!

By the way: All advice here is without guarantee! The user is responsible for what they do!