Why undyed leather ages better

Most leather is dyed for a reason: it hides the differences between one part of a hide and another. Undyed leather does not hide anything, which is exactly why it is worth using.

What happens in the first year

Undyed vegetable-tanned leather darkens where it is handled and stays pale where it is not. A card case will show four distinct tones after a year: nearly black at the folded edge, honey across the body, and pale at the stitching.

What to avoid

Sunlight and water, in that order. A week on a windowsill will do more than a year in a pocket, and it will not be even.