Note that this process works best when used with vegetable tanned leather. You can technically stiffen the leather by soaking it in nothing but room temperature water, but it will only become mildly harder and you will not be able to shape it. The addition of a hot water step will allow you to make structural changes while hardening the leather further.
Use an accurate thermometer to keep track of the temperature. If the water is too hot or too cold, your results can vary dramatically from those described here. If you do not have a thermometer, you can gauge the temperature of the water by slowly heating it on the stove and testing it every minute or so with your bare hand. If you can keep your hand immersed in the water, it is safe to use that temperature for your leather. Once you can no longer bear to keep your hand in the water for more than an instant, remove the water from the heat source and do not allow it to get any hotter. Some people prefer to soak the leather in boiling water. Doing so stiffens the leather at a faster pace, but it also gives you less control. The resulting leather can become very brittle and may be unevenly stiff across its surface.
After the first minute, you should already see the leather darken and curl. The longer you soak the leather, the stiffer it will become. If you soak the leather too long, however, it will be more brittle when dry. When using this method, soaking the leather in hot water for 30 seconds after it already darkens will result in a piece of leather that is hard but not inflexible. This means that the total hot water soak time would be about 90 seconds. Leave the leather in the water for a longer period of time if you want to make it stiffer.
When wet, the leather will be stretchy and easy to form. This stretchiness will vanish within the first minute or two, though, so you need to work fast if you plan to stretch it out. The leather will still remain flexible for up to an hour after the stretchiness fades away, though.
Stiffened leather will also shrink, so the piece you started out with may not look as large when you finish the process.
This process is generally recommended for use with vegetable tanned leather. The amount of time you leave the leather in the water will vary based on the thickness and quality of the leather. Usually, leaving it in the water for 10 to 30 minutes will suffice. The leather should be notably flexible when you remove it.
Move the racks of the oven around as needed to clear enough room for the leather piece. If your oven does not reach a temperature this low, simply use the lowest temperature available. Note that higher temperatures could cause a little steam scalding, however, which may alter the color and cause more greater shrinkage.
Since the leather is still fairly cool at this point, it may not keep its form when left alone. After shaping it, you should hold the new forms in place using string, stitching, or nails.
You can let the leather remain in the oven even after it dries out, but know that dry baking it will cause the temperature of the leather to rise and the structure of the leather to become both harder and more brittle. [6] X Research source
Once cool, you should remove any string, thread, or nails holding the shape in place. If the leather has become sufficiently stiff, it should be able to hold its new form on its own now.
Make sure that the racks inside the oven are rearranged as needed so that the leather piece can fit inside without brushing against the racks or the sides of the oven. This method should work well with most types of leather, but vegetable tanned leather is still the easiest to work with. Also note that it tends to be a good method to use if you are trying to stiffen leather than has already been formed and does not need any additional shaping.
The heat itself plays an important part in the stiffening process. Essentially, it liquifies some of the molecules in the leather, causing them to break down and become more flexible. When those molecules solidify again, they do so in a structure that is even harder than the leather’s original chemical structure. If you allow the leather to get too hot, however, it can become too brittle by the end of the process.
Beeswax is the wax of choice, but you can use melted candles or nearly any other type of wax, as well. To melt the wax: Heat 1 to 2 inches (2. 5 to 5 cm) of water in the bottom part of a double boiler placed on the stove over medium-high heat. Place the wax inside the top part of the double boiler. As the wax begins to melt, stir it with a disposable spoon or chopstick. Continue until the melts completely.
The leather should soak up the hot wax. If it does not do so, the leather is not yet hot enough and should be returned to the oven. Continue brushing the wax onto the leather until the leather cools and no longer absorbs the wax.
You should repeat this process until the leather no longer absorbs any more wax, even when hot. One way to tell that the leather can no longer absorb wax is to look at the coloring. The wax will alter the color of the leather slightly. If the entire surface of the leather is an even color, it has likely absorbed as much wax as possible throughout the entire piece.
