The white powder on your leather boots is most likely spew, also known as bloom.
What is Spew?
Spew isn't mould or mildew, though it's often mistaken for them. According to experts, spew refers to the migration of fats or oils from within the leather itself. These fats and oils travel to the surface and, when they come into contact with the air, they crystallize. The crystals then form on the surface as a white powder or a "bloom."
This process is more common in natural or minimally treated leathers that retain more of their original oils and fats. Temperature and humidity changes can sometimes encourage this migration and crystallization.
Spew vs. Mould: How to Tell the Difference
It's important to distinguish spew from mould, as the treatment is different.
| Feature | Spew (Bloom) | Mould |
|---|---|---|
| Appearance | Crystalline, powdery, sometimes waxy deposit. | Fuzzy, powdery, or slimy. Can be white, green, black, or other colours. |
| Texture | Brushes or wipes off easily. Feels waxy or greasy when rubbed. | Smears or spores might spread. Can feel fuzzy or dusty. |
| Odour | Usually no significant odour. | Often has a musty, damp smell. |
| Location | Tends to form evenly over surfaces, or in patches. | Can appear in spots, especially in areas of high humidity or where dirt is present. |
| Cause | Migration of fats/oils from within the leather. | Fungal growth from external spores, usually due to moisture. |
The key indicator for spew is that it tends to brush off easily and feels somewhat waxy or greasy when rubbed between your fingers, and it lacks the musty smell of mould.
How to Remove Spew
Removing spew is usually straightforward:
- Gently Brush: Use a clean, soft brush (like a horsehair brush) to gently brush off the white powder.
- Wipe: If brushing doesn't remove it completely, use a soft cloth, possibly slightly warmed (a hairdryer on a low setting aimed at the cloth works well) to wipe the surface. The gentle warmth can help re-melt the surface crystals, allowing them to be absorbed back into the leather or wiped away.
- Buff: After wiping, buff the leather with a clean, soft cloth to restore its finish.
Avoid using water or harsh chemicals, as these can potentially damage the leather.
Preventing Spew
While not always preventable, especially with natural leathers, proper care can help:
- Storage: Store your leather boots in a cool, dry, and well-ventilated place, away from direct sunlight and extreme temperature fluctuations.
- Conditioning: Regularly cleaning and conditioning your boots with appropriate leather products can help maintain the leather's health and potentially reduce the likelihood of oil migration.
Understanding that the white powder is likely harmless spew means you can address it with simple cleaning rather than worrying about fungal damage.
