@Shihali so, other than aesthetics, staining the cartridge is basically harmless. It stains because the cartridges are made of polypropylene. You could just put another ink there despite the stain and it would be fine, you probably wouldn’t notice if it were an ink that was in about the same color range like a blue.

The converters do not stain as easily and you can take them apart and clean them with a pipe cleaner if that’s what you prefer.

@Shihali have you let the ammonia sit inside the cartridge overnight? Or how did you use it?

@01189998819991197253 Lamy Safaris are list price 20€ but they often go on sale during back to school and I’ve seen them go as low as 10€. You could also consider Faber Castell Grip which is similar pricing and I see it for 12€ on Amazon.de right now.

If you want to truly go budget, I recommend the Platinum Starlet (also know as Meteor) from AliExpress, for around 4-5€.

For all of the above I would suggest F which is around 0.5. M is around 0.7.