>>> There are a lot of dark areas and some kind of texture on the chairs.
These rough textures are the deteriorating of the leather reverting to rawhide. The strength of the leather is the grain or outer surface, while the deeper it goes to the other suede side the weaker the tensile strength of the leather is. This alkaline overexposure from sweat has to be severely pH balanced and original fatliquor (fat and oil) replenished to restore back the integrity of the leather. And during the drying process, without sufficient fatliquor (or the leather does not have sufficient ionic positive (+ve) charged strength) it may become too stiff that it tears the leather apart. Remember that leather is an amphoteric protein material, and in this situation needs to be charged with a low pH rinse like Acidifier-2.0 (pH value 2.0). The stick together leather fiber within the leather structure will need to be opened up to receive the Fatliquor-5.0.
My recommendation is for you to understand the risk of restoration when the leather integrity has become too bad. I am available for online consultation or coaching if you want to email me. Until you understand the risk involved, before beginning your restoration.
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Roger Koh
Leather, Skin, Hair, Eye & Acne Care System Formulator
Consultant / Practitioner / Instructor / Coach
web: www.leatherdoctor.com
forum: www.leathercleaningrestorationforum.com
email:
[email protected]