Sometimes nothing is not an option. Have a friend that is a Luger collector, and several years back he bought one of the 1900 7" Lugers with original shoulder stock and holster. The pistol and holster had been in a bank lock box for approximately 30 years, and the holster was dried out to the extent the original glazed surface was flaking off. He carefully wrapped it in a soft cloth, but every time the cloth was unwrapped more of the leather surface had flaked off. Finally in desperation he treated the holster with Pecard's Antique Leather Dressing, and now the leather is stabilized.
On page 29 of Kenyon's "Luger: The Multi-National Pistol" there is a pistol and holster identical to my friend's except the one pictured does not have the shoulder stock. The holster shown has the same flaking problem that my friend's did.
Neatsfoot oil is death to leathers you wish to preserve. My dad believed it was good for everything, and treated this Randall knife sheath with it about 35 to 40 years ago. Today the sheath is very black and the leather is coming apart. The leather around the snap has almost completely deteriorated, and the rest is soft and flaky. The sheath was one of the old Johnson sheaths which were a beautiful light russet when new.
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