February 29 - everyday carry artisans

When mould grows into leather, usually it does not cause major damage.  The mould soaks up its food from the parts of the leather that do not contribute to strength. In fact, until the mould starts to grow new spores, it is effectively invisible – you cannot tell it is there.

The biggest problem with moulds in leather is caused by a change in color - staining. Often they stain the leather in bright colors, and leave spots and grain marks that will make finished leather look inferior.  This causes downgrading of the finished product, and can cost a lot of money.

Once moulds are inside the leather, simply cleaning the surface will not solve the problem, since the moulds will grow right out again.

Moulds can also consume some important additives used in leather making, such as fat liquors, tannins and so on.

How to slow down mould growth?

If we understand the things moulds need to grow, we can change these things, and slow down growth.

1. Water.  Mould will not grow on dry materials.  If finished leather is dried and kept dry, there will be no mould.  However, allowing leather to get wet will encourage mould growth.  Leather in the wet blue state is very prone to mould growth.

2. Acidity.   Mould grows best when it is in a slightly acid environment.  Pickled pelts are too acid for fast mould growth.  Very alkaline conditions do not support much mould growth.

3. Warmth.  Mould likes it best between 25 and 30 deg. C.  That is why it is worse in summer, or in the tropics.  Keeping leather stored in cool conditions will not stop mould, but will slow its growth a little.

4. Oxygen.  Without oxygen, moulds cannot grow.  If wet blues or pickled pelts are baled and pressed into a tightly packed state, mould will only grow on the outside.  There is too little oxygen inside the pack.

5. Nutrients.  Moulds soak up the soluble parts of leather as food.  Unfortunately, we cannot remove these to control mould growth.  Some leathers (like vegetable tanned leathers) have more nutrients, and support especially vigorous mould growth.

Aniline is a transparent dye that is drum dyed with leather and because the finish is transparent and shows the natural markings of the leather, only the best quality hides can be used.

Semi-Aniline leather is pure aniline leather that has a small amount of pigment or clear finish thus allowing the natural characteristics of the hide to still show through while offering some of the benefits of color consistency and increased wear ability.

So how do we identify them?

Here are some tests we can use :

1.  Water Test

Drip a small amount of water on to the semi-aniline leather. It will sit on the surface so dab it with a piece of cloth to absorb the liquid. You will notice that the leather will absorb a very small amount of water, this shows by a slightly darker patch. It can take around 3 minutes for a semi-aniline to absorb a drop of water.

2.  The Magnifying Glass Test

Looking at a semi-aniline leather through a magnifying glass will look quite similar to an aniline. The hair follicle holes are slightly visible like craters or human pores but you will notice a thin pigmented coating covering them. Some semi-anilines have thicker coatings than others and so the holes may not always be identifiable.

3.  The Visual Test

The color of a semi-aniline will look quite uniform, not as varied as aniline and not as uniform as pigmented. The grain pattern will be natural looking as only a thin pigmented coating is applied. You may be able too see natural markings, but you will have to look closely to spot them. A semi-aniline is often two toned but this two tone effect can sometimes be very slight and so hard to spot.

If you do not maintain the leather using the leather conditioner, the top coat of color can wear off in high use areas. To make the leather last longer, apply the protection cream once every three months to reduce friction and so, stop the color wearing away as quickly.

4. The Touch Test

Semi-aniline feels quite natural and soft to the touch. The finish is often smooth and you can feel the lacquered surface, which makes the leather semi slippery compared to a pure aniline piece.