Since vachetta leather is without a finish it is highly absorbent and darkens when it is wet.
Generally an acidic solution will lightens it up when dry again and an alkaline solution will darkens it.
In this case the cleaner used could be too alkaline for the vachetta leather.
Vachetta leathers is acidic having a pH of 3 5 and any cleaning solution within this pH range will be safe for this leather type.
To rectify the darkening stains from an alkaline cleaner is to neutralize it with Acidifier-2.0 (pH 2.0)
Degreaser-2.2 is a water based degreaser that has a pH of 2.2.
It is developed to remove penetrated darkens grease stain especially from body contact, follows with Rinse-3.0 (pH 3.0).
Vachetta leather will darkens when exposed to sunlight just like our skin.
dTarnish-1.3 (pH 1.3) will lightens up the tanning effect, follows with Rinse-3.0.
So there are three possibilities that vachetta leathers will darkens up mentioned above, from: Alkaline overexposure, Grease & oil, and Sunlight and their matched solution.
The common blue jean stains is removed by Prep-4.4 (pH 4.4) follows by Cleaner-3.8 to remove the sticky residue and Rinse-3.0.
Below is the problem solving guide for vachetta leathers.
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Leather-Safe Problem Solving Guide-V9 - Vachetta
See the kits in this link:
http://www.leathercleaningrestoratio...splay.php?f=22