Making GLUE from animal SKIN - used for thousands of years - STRONGER than modern glues?

In this video I make a glue from rabbit skin. The adhesive strength is absolutely amazing.
This type of glue made from animal skins is also called glutinous glue and has been used for thousands of years.

The whole production process is filmed in detail and subtitled.
It is intended to record my current knowledge.
Today, these glues are still used in instrument making (violin, cello, etc.). The high adhesive strength and removability for repair are appreciated here.
They are water-soluble, which can be both an advantage and a disadvantage.

I need this glue for my two following YT-projects.


Production process - Additional information on the film:

Preserving skins:
Drying and thus preserving the skins has proven to be very practical. Glue production can be started at any time.
Scraping off fat and meat residues is easiest with such thin skins (rabbit) when dried.

Lye:
Making lye with ash was the easiest way for me.
Today, the industry uses a lye solution (milk of lime) made from slaked lime. The soaking time for cattle hides is up to several weeks.
The lye converts the collagen into glutin and dissolves fat and meat residues.
The soaking time in the ash lye has proven to be sufficient for rabbit hides, with a total of 24 - 36 hours, depending on the thickness of the hide.

Acid:
The acid is used to neutralize the remaining lye in the skins. I simply used vinegar. It worked well. The industry uses more aggressive acids.

Boiling out:
The glutin is boiled out of the skins in 3 stages.
1st stage at approx. 65°C (149°F) for one hour.
2nd stage at approx. 75°C (167°F) two hours.
3rd stage at approx. 85°C (185°C) for two hours.
The glue from the 1st stage is of better quality than from stages 2 and 3.

Filtering:
Thick cotton filters are used in the industry. The cloudy brew is pressed through with pressure. The result is a clear liquid. I can't think of anything better than a coffee filter. The result is not very intoxicating. The brew is still cloudy. Nevertheless, the glue quality is good!

Breaking test:
I was extremely surprised and pleased that the home-made glutinous glue has a higher adhesive strength than the modern glues tested (white glue, PU glue, epoxy resin).
The secret lies in the possibility of priming the glued surfaces before gluing, which prevents the glue from sinking too much into the wood. This is hardly possible with any modern glue.
Nevertheless, with ALL glues the glue bond is still stronger than the wood strength along the grain.

Link to the breaking test (additional test):
https://drive.google.com/file/d/1GWmT...


0:00 Intro
0:28 Preparing and drying skins
1:14 Scrape off skins
2:15 Making lye
3:32 Skins in lye
4:13 Remove hair
5:27 Neutralize with vinegar
6:29 Cut small
6:53 Boil out
9:39 Dry gelatine
10:00 Wooden blocks for breakage test
10:25 Glueing with modern glue
11:56 Prepare skin glue
13:50 Breaking test