I’ve been asked whether immersing a glove into water is a good or bad idea. Let’s take a look at the chemistry. Dunking leather into water does two things chemically.
1. When leather is wet it becomes more malleable. This means you can shape the mitt more easily, creating a pocket that works for you. As the leather dries, it will retain that shape. However, as the water evaporates, the internal fiber structure of leather tightens as the fibers shrink. This then has a stiffening effect. The leather's suppleness degrades. The temperature of the water matters. The warmer the water the more stiffening the effect.
2. There will be a pH differential between the alkalinity of tap water and the acidic nature of leather. When two elements of differing pH contact each other, a reaction occurs. This reaction damages leather. However, leather is a highly durable material and can take a bit of abuse yet still perform as expected. Nonetheless, there is damage done, even if it's slight.
There are two schools of thought. The Japanese have preached for years to do the dunking method to quickly develop a desired mitt shape. Whereas the glove manufacturers discourage it as it does have negative consequences.
Here are the details...
The answer lies in the chemistry of leather in two ways - the interaction of water with the internal natural oils and collagen fibers and the leather's pH.
Collagen and Natural Oils: Water is a polar molecule, and while the natural oils and added fatliquors in leather are non-polar, the water manages to interact with them and the surrounding collagen fibers. As the water permeates the leather and then begins to evaporate, the water molecules create temporary bonds with these natural oils. As the H2O leaves the leather, it pulls the lubricating oils out with it. This stripping process leaves the microscopic collagen fibers within the leather dry, unlubricated, and tangled. Since the fibers can no longer slide smoothly past one another, the material can become rigid, brittle, and eventually prone to cracking.
pH Damage. The average tap water in the US has a pH of 7.5 which is slightly alkaline. The typical pH of leather is 4.5 to 5.0 which is acidic.
When two elements with different pH levels meet each other, a chemical reaction occurs as the pH level of both elements neutralizes the other. This reaction damages the fiber structure of leather. As a leather expert with 35 years of experience doing leather repair and restoration, correcting pH induced damage is a common problem. I have a ton of photographic evidence. Besides that, the evidence is in your own home. You can do this test yourself. All soaps (with rare exceptions) are alkaline. Your skin, (which is what leather is), is acidic. Intuitively you know this is a bad idea but it makes the point. Wash your face, particularly with a highly alkaline dish detergent, and don't rinse the soap off. Your skin will begin to chaff. This is a function of the pH differential. The fiber structure of the epidermal layer of your skin will break down due to the pH induced chemical reaction. The difference between your skin and leather is your skin is a living organ that can regenerate skin cells to replace the pH damaged cells. On the other hand, the cow is dead. The leather can't regenerate if it suffers pH damage.
Here's the basics...
The pH scale determines the relative alkalinity or acidity of an aqueous (water friendly) material. Pure water is considered neutral and has a value of 7.0. The scale is logarithmic which means, each whole number higher or lower than 7 is factored by 10. So, a pH of 6 is 10 times as acidic as water, 5 is 100 times acidic, 4 is 1,000 times, etc. When two elements with differing pH contact, they neutralize. This reaction can be mild if the 2 elements have a pH that is close to each other, or violently reactive if they are far apart. I wouldn't recommend dunking as there are lots of alternative ways to break in a glove that don't cause any damage like the use of Advanced Leather Solution’s Mitt-Spit Break-in product.
A one-time dunk is likely to do very little damage, but you can't say zero. Repeated exposure to pH damage however has a cumulative corrosive effect.
If you do plan on dunking, then the recommendation is a combination of a dunk and when the leather is dry again, apply Mitt-Spit Break-in (pH consistent with leather) to replace the lost oils, and boost suppleness. This combination strategy corrects the natural oils loss and adjusts the pH.