The Staedtler Mars Professional High Precision Ink Pen Ink Refill in 0.5 and 0.35 sizes is a premium quality ink product manufactured in Germany by Staedtler. Tested the ink in the pen and it works.
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These were bought new by me and never used apart from testing them out when I first got them. I've included writing samples in the photos. All the cartridges still write but they do look to be drying out. It's possible some rubbing alcohol would help but I'll leave that to the new owner. If you have any questions please let me know.
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Overall this Pen is in good condition.
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1pc Staedtler Mars Lumograph Sketching Pencil Artist Professional Drawing Graphite Pencil 12B-10H
Aliexpress UK
2.0 Retractable Mechanical Metal/Plastic Pencil Colored Black 2mm Refill 2B Lead Professional Pen
Aliexpress UK