Fatty spue - Fat marks on leather
"Fatty spue" is a type of stain caused when residual fat from the leather reacts to fluctuations in temperature and humidity. It appears as a whitish patina or coating, which at first glance looks like white mould. The causes of fat or grease marks on the leather surface are different and affect several steps in the tanning process. Inadequate degreasing of natural fats in the skin, as well as the oils and fats used for rehydration can lead to fat rashes.
Unfortunately for the tanner, this phenomenon does not arise immediately after the production of the leather, but weeks later. Most of it happens in transit or when the leather items are packed in plastic. Changes in humidity play a big role and once fatty spue shows up on the surface, it will keep appearing, despite regular cleaning.
Unlike with mould, heating can make fat temporarily invisible.
There are two main circumstances where fatty spue is most likely to occur. Firstly, fat marks are common in new leather which has been manufactured in Asia and transported in containers over long distances. If the goods have been packed in plastic in areas of high humidity, this will cause the excess fats to sweat out. In most cases, the complete shipment is affected.
The second scenario involves old leathers that have been treated with waxy care products. Excess sweating can occur when temperatures or humidity go up, leaving fatty marks.
Often fatty spue is mistaken for mould. There is a simple test for differentiating between the two. If you apply a hair dryer to the affected area, the wax or grease melts and disappears temporarily, whereas mould would remain unchanged.
Light fat marks can be kept under control with this method. After a single treatment with the hair dryer, the fat will have almost disappeared as it reacts quickly to heat.
After one-time treatment with the hair dryer, the greasiness is almost gone. Grease on leather reacts quickly to heat.
For treating light fat stains on water-resistant leathers, the following procedure is recommended: Clean the leather with a mixture 1:10 of COLOURLOCK LEDER FEIN LEATHER AND FUR WASH CONCENTRATE and water. Apply thin layers of the solution using a wet cloth and let dry on its own or use a hair dryer to speed up the process. Protect the surface with the COLOURLOCK LEDER FEIN LEATHER CARE AND WATERPROOFING OIL. Although this cannot guarantee that the problem will not reoccur, this method is much faster than the constant blow drying and wiping. More solid fat or wax which causes the stain is diluted gradually and loses its effect.
Fatty spue on a satchel.
Cars with fat marks: Toyota, BMW Mini, VW Beetle.
In the last few years, the problems of fat marks on leather furniture have increased.
At first glance not clear, but tests revealed they were fat marks.
Testing fatty spue
This test has been developed by Gerber Anderas Ollert. Even if he was not scientifically verified, his testing work has always been helpful.
- Add 50-100 ml of tap water in a 500ml lab beaker with a large opening.
- Cut a piece of leather to be tested so it fits the beaker. Fix the leather with a rubber band over the opening of the beaker. The leather piece should also fit into the container.
- Place the leather with the grain side upwards and close the beaker with it.
- Heat the water and cook for 2 minutes or longer if the leather is thick. Steam should emerge from the visible scars.
- Place the leather piece inside the empty but still wet beaker and close it airtight with plastic wrap and a rubber band.
- Leave for 3-5 days at temperatures from 20-25°C. If the leather hasn’t developed any fat marks during the test, then no fat rash is to be expected by the end customer.
Other leather damages
- Typical leather damages such as aging, fading, grease stains, discolouration etc.
- Dye transfer from leather
- Typical damage to PU leather in the furniture area
- Flamingo effect: Reddish discolourations on bright furniture in concealed areas
- Bronzing: Metallic glimmer on new leather
- Glue migration from the back side to the visible side of the leather
- Mouldy leather