To harden the skin you have to alter its structure on a molecular level. This is normally achieved by combining the use of heat, water and wax, but there are many procedures for doing this.
Steps
Method 1 of 3: Water Absorption
Step 1. Soak the skin in cold water
Take a large bucket or basin and fill it with cold or room temperature water. Soak the skin for about ten minutes or until it is completely soaked.
- This process gives the best results on vegetable tanned leather.
- Technically you could harden the skin by just soaking it in water at room temperature, but the skin would be only slightly harder and you would not be able to shape it. Adding boiling water will allow you to modify the fibers and promote greater hardening of the skin.
Step 2. Heat a second pot of water
While the skin is soaking, fill a large enough container with water and place it on the stove over high heat. Continue heating the water until it reaches a temperature of 82 ° C.
- Use a precision thermometer to check the temperature. If the water is too hot or too cold, the results can be totally different from what is described here.
- If you don't have a thermometer, you can check the temperature of the water by heating it slowly on the stove and feeling it every now and then with your bare hand. If you can keep your hand submerged in water, that temperature will be good for the skin. If, on the other hand, you can't keep your hand in the water for more than a moment, remove the pot from the heat and stop heating.
- Some prefer to soak their skin in boiling water. This method actually hardens the skin faster, but you would not have a good control of the process and the result would be that of having a very fragile skin with uneven degrees of hardness.
Step 3. Soak the skin in boiling water
Remove the skin from the cold water and immerse it in boiling water. Leave it for a few minutes.
- After the first minute you should already see the skin darken and wrinkle.
- The more the leather remains immersed in water, the more its degree of hardness will increase. But if you leave it too long, it will dry out and it will tend to become more brittle.
- With this method and leaving the skin in hot water for another 30 seconds after it has darkened, you will get a firm skin but still with a certain degree of flexibility. This means that the total immersion time in boiling water should be around 90 seconds. Leave it in the water longer if you want it to be harder.
Step 4. Give it the shape you want
Once out of the water, the skin should be quite flexible. If you need to shape it into a certain shape, now is the time to do it.
When wet, the skin is very supple and easy to shape. However, the elasticity will tend to disappear after a minute or two, so work quickly if you need to extend it. When the elasticity has disappeared, the skin will still have some degree of flexibility for an hour
Step 5. Let the skin dry at room temperature
Leave the skin to rest at room temperature for several hours. Once dry, the skin should be clearly thicker and firmer.
Hardened skin shrinks, so the piece you started with will likely be smaller once you finish the process
Method 2 of 3: Cooking
Step 1. Immerse the skin in water at room temperature
Fill a basin, bucket, or equivalent container with cold or room temperature water. Soak the skin and leave it until it is completely soaked in water.
- This procedure is usually recommended for vegetable tanned leathers.
- The duration of immersion in water depends on the thickness and quality of the leather. It is usually sufficient to leave it in the water for 10 to 30 minutes. When you remove it from the water, the skin should be considerably more flexible.
Step 2. Heat the oven
While the skin is soaking up with water, preheat the oven to 50 ° C.
- Remove or move the grates out of the oven and make enough space for the piece of leather.
- If your oven does not reach such low temperatures, use the lowest temperature available. Keep in mind that higher temperatures can cause some searing steam which could alter the color of the skin and increase the shrinking effect.
Step 3. Shape the skin as you wish
Remove the skin from the water. If you plan on giving it some shape, do it now while it is flexible and easy to handle.
At this point the leather is still quite cold, and once released it may not hold the shape you gave it, so after modeling it consider whether you need to keep it in shape with string, thread or nails
Step 4. Cook the skin
Take the moist, molded skin and bake it until it feels dry. This can take 20 to 90 minutes, depending on the amount of water absorbed by the skin and the temperature of your oven.
The skin can stay in the oven even after drying, but keep in mind that dry cooking will raise the temperature of the skin and make its structure more fragile and harder
Step 5. Let it cool down
Remove the hot, dry skin from the oven and let it cool to room temperature until you are able to handle it with your bare hands. Meanwhile the skin will continue to harden.
Once it has cooled, remove the ropes, threads, or nails that held it in shape. If the skin is stiff enough, it should now stay fit on its own
Method 3 of 3: Wax
Step 1. Heat the oven
Turn on the oven and bring it to a temperature of 90 ° C.
- Make sure that the gratings inside the oven are arranged so that the skin can enter without rubbing them and without touching the oven walls.
- This method should work well with any type of leather, but vegetable tanned leather is easier to work with. This is also a good way to harden skin that has already been molded and does not need to be put back into shape.
Step 2. Cook the skin to dry
When the oven has reached the indicated temperature, insert the skin and let it cook for 30 minutes. When you take it out of the oven it should feel very hot to the touch.
- Heat plays an important role in the hardening process, liquefying some of the molecules in the skin which will crack and become more flexible. When these molecules return to their solid state, they do so in a structure that is more rigid than the skin's original chemical structure.
- But if you let the skin get too hot, it could become brittle at the end of the process.
Step 3. Melt some wax
Put a block of beeswax in a double kettle and heat it until melted. Do this while the skin is cooking, so you will have both skin and wax hot at the same time.
- Beeswax is the best choice, but you can also use liquefied candles or any other type of wax.
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To melt the wax:
- Heat 3-5 cm of water from the bottom of the kettle on the stove over medium-high heat.
- Put the wax in the top of the kettle.
- When the wax begins to melt, mix with a disposable spoon or toothpick and continue until completely melted.
Stiffen Leather Step 14 Step 4. Apply the wax to the skin
Remove the skin from the oven and spread it out on some newspaper. Take a rather large brush, dip it in the melted wax and pass it evenly over the skin.
- The skin should absorb the hot wax. If it does not, it means that it is not ready yet and that it must go back to the oven.
- Keep applying the wax until the skin cools and can no longer absorb it.
Stiffen Leather Step 15 Step 5. If necessary, heat the leather and apply a second coat of wax
After the first coat of wax, return the skin to the oven and heat it for another 20 minutes. Then remove it from the oven and brush the surface with another coat of liquid wax.
- Repeat this procedure until the skin, even if heated, will no longer absorb wax.
- One way to determine that the skin has reached its wax absorption limit is to look at its color. The wax slightly alters the color of the leather, so if the surface has a uniform color, the leather has probably already absorbed as much wax as possible.
Stiffen Leather Step 16 Step 6. Let it cool completely
Let it cool and dry completely. The leather should now be very hard and almost impossible to bend.
