Fine ground Turkish Emery.
This is the same emery used in emery boards and those little strawberries that come on some 'tomato' pin cushions. Emery sand has long been known to sharpen needles but it also cleans them. We like to call it "Sharpen & Shine". Our 'French' square bottle has a slender neck to pour easily into your pin cushion.
Open since 2005, but currently online only, A Threaded Needle is located in British Columbia, Canada. I am always happy to hear from you by e-mail firstname.lastname@example.org