Those Interesting Tales About Shoe Glue

   Today, if we need to glue something, we can easily grab super glue, strong adhesive, or all-purpose glue. But in ancient times, without chemical plants or synthetic resins, what did people use when a shoe sole came apart?

The answer is: Millet Glue (Shǔ Nián Zǐ). It might be one of the earliest shoe adhesives with clear written records in Chinese history – the Tang Dynasty's version of super glue.

I. How did a bowl of “porridge” turn into glue?

The name "Millet Glue" basically reveals its recipe. “Millet” refers to a type of grain; after hulling, it becomes yellow millet, which is sticky when cooked. "Glue" means something that sticks things together. So millet glue is simply a special paste made by grinding yellow millet into powder and mixing it with boiling water.

You might think: Isn't that just flour paste? You're right – in principle, it's the same family as the paste we used to stick couplets on doors as kids. But here's the difference: Tang Dynasty craftsmen discovered that paste made from millet was stickier, tougher, and harder after drying than ordinary flour paste. When used to glue the lining inside shoes, it dried as stiff as cardboard, helping the shoe keep its shape without damaging silk or brocade.

So this bowl of “millet paste” was a legitimate industrial adhesive in its time, not just a kitchen leftover.

II. What could it stick, and what were its drawbacks?

Millet glue's main battlefield was inside shoes. Tang Dynasty cloth shoes (especially those worn by officials and scholars) needed to be crisp and well-shaped. Between the upper and the lining, there was a layer of “stiffener” – multiple layers of fabric pressed together to form a skeleton. The glue that held this skeleton and the fabric layers together was millet glue.

Its advantages were clear: completely natural, non-toxic, and non-corrosive to fabric. Compared to the bone glue made from animal hides and bones later used in Europe, millet glue was much gentler on silk.

But its drawbacks were also obvious. First, it feared water – it softened when wet, and if soaked for too long, it would revert to paste. Second, it feared humidity – if left through a rainy southern summer, the shoes would come apart on their own. Finally, its durability was mediocre: after two or three years, it would naturally age, become brittle, and the shoes would unglue anyway. In other words, millet glue was only suitable for cloth shoes worn indoors in dry areas. If you wore them through puddles, the soles would soon "open their mouths."

III. Why is it considered “the earliest glue”?

When we talk about "the earliest glue", there are actually several branches: bone glue (from animal hides and bones), tree resin (pine resin, peach gum), and starch paste. Millet glue is a representative of “starch-based natural adhesives”.

Its working principle is very similar to white glue: solid particles (starch) are dispersed in water; after application, the water evaporates, and the particles gather together to form a solid film, “holding” the two surfaces together. The only difference is that white glue uses synthetic resin, which sticks more strongly and is more waterproof.

Looking at the timeline, the use of millet glue during the Tang Dynasty (7th–10th century AD) is clearly documented, predating the large-scale industrial application of early bone glue in Europe by several hundred years. So calling it the “Tang Dynasty super glue” is no exaggeration.

IV. From a bowl of millet paste to today's shoe glue

It took us over a thousand years to go from millet glue to modern water-based polyurethane shoe adhesive. Today's glues are waterproof, heat-resistant, and capable of bonding rubber and leather. But looking back, the ancients used the grains at hand to solve everyday adhesion problems – that kind of resourcefulness with local materials is truly impressive.

Next time you glue something with super glue, think about this: over a thousand years ago, a Tang Dynasty cobbler holding a bowl of sticky yellow millet porridge was doing exactly the same thing as you.