I used ammonia to make a patina on my Kaweco Liliput. Here's the result (I also changed its nib and bought a brass clip for it). I'm not sure if I like
Kaweco Liliput Fountain Pen - Stainless Steel — The Clicky Post
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Kaweco Liliput Fireblue Clone: Delike Element 'Titanium' - China, Korea and Others (Far East, Asia) - The Fountain Pen Network