Not all leatherworking projects can be completed by stitching or gluing individual pieces together; in some cases, the material needs to be shaped as one piece. Fortunately, since leather is a naturally pliable substance, it is possible to shape and mould it into a very wide variety of forms. Leather moulding projects can be quite simple or extremely advanced, but in all cases is done using the same very basic process.
The basic required first step for any leather moulding project is soaking the leather in water to make it easier to shape and more capable of holding its shape. Depending on your project, you may do this in a number of ways. The first consideration is the temperature of the water; the hotter the water is, the more stretchy the leather will be immediately after soaking. However, hot water will also cause the leather to shrink somewhat and harden as it dries, and the higher the temperature the greater this effect will be. You will probably want to experiment with different water temperatures to decide what is best for your project. In all cases, the leather to be moulded needs to be submerged in the water long enough to be soaked all the way through. If the water is only lukewarm, just leaving the submerged leather in for a few minutes is generally fine, and if it is hot, a good indicator is when the leather stops producing bubbles. The hotter the water, the less time is needed; most craft leather will be thoroughly soaked in near-boiling water in less than 30 seconds. As with adding heat, adding to the length of time the leather soaks in hot water will contribute to the shrinkage and hardening as it dries.
After you remove the leather from the water, immediately start moulding it into the basic shape you want. When the leather is still hot and wet, it is stretchy to some degree, but it loses this quality very quickly as it dries, so you may need to work fast if you are stretching the leather out. The longer it dries, the stiffer the leather will become, but for most moulding work soaked leather will continue being sufficiently pliable, if not stretchy, for quite a while after being removed from the water. If you plan on tooling your moulded leather at all, do so once it is dry enough to no longer be dripping or forming pools on the surface when squeezed, but still damp and pliable. Once it hardens into its final moulded shape, tooling will become much more difficult.
Once the leather is in the correct shape, you'll need to let it sit overnight to fully dry and harden to whatever extent it will. During this time, be careful to keep the leather held in its intended shape, and be very cautious about anything touching the leather that may leave a mark on it. Just about anything that applies pressure to the wet leather will leave a permanent mark, so you may need to cushion your piece if its shape is being supported by a hard rig for drying. Once the leather has dried completely, you can continue to work with it or, if need be, repeat the process if the results are unsatisfactory. If you repeat the soaking and moulding process, though, the leather will shrink and harden more each time, so try to avoid doing so if possible.