Casein glue is a type of adhesive made from milk protein. The glue is known to be very strong over a long period of time and is highly resistant to water. It has a drying time that allows enough time for pieces to be positioned accurately. The process of creating this glue is nearly identical to that of making cheese and can easily be performed at home. Although most adhesives are based on synthetic chemicals, casein glue still enjoys use as a natural binder.
There have been many uses for casein glue throughout history. There are records that show it was created and used by the ancient Egyptians. It was employed in the Middle Ages to bind together thin panels into thicker plates on which artists could paint. It also is believed to be used by makers of famous musical instruments that have lasted for a century or more. It was used extensively in woodworking, furniture making and even to assemble early wooden aircraft.
While casein glue can be purchased commercially, it also can be made at home with similar results. The process involves heating milk and then adding an acid such as vinegar to separate the curds from the whey. The curds are taken out of the excreted liquid and mixed with baking soda to neutralize the acid. The remaining liquid from the curds is removed by pressing them under a heavy weight. The final result is a white paste-like substance that will become a powerful adhesive when dry.
If one is making casein glue at home, it should be noted that the fat content of the milk plays a part in the strength of the glue. Milk that has a high fat content, such as whole milk, will produce weaker glue than non-fat and low-fat milks. This is because the fat in the milk prevents the casein from polymerizing.
In addition to being very strong and having a long lifespan, casein glue is also very water resistant. Unlike some adhesives, water will not weaken or dissolve casein. In some cases, however, water that comes into contact with the adhesive can pass on microorganisms that will eat the glue and eventually destroy it, but this is not a function of the water itself.
The drying time of casein glue can be a benefit in many situations. It takes a long time for the glue to properly cure and harden. This can allow the assembly of multiple complex parts that might need to be moved during assembly before securing them to allow the glue to set. This also might be a disadvantage for projects that require something that sets more immediately.