Platinum - Carbon Ink - Black Cartridges

Please be very careful when using this ink and we do not recommend using in your valuable, vintage or precious pens - The ink is ideally to be used by experts that know how to handle the ink. Due to the carbon in the ink, it can clog and block feeds, so we advise that you should use it in pens you use daily. If not we advise that you flush your pens if left unused for more than two days using this ink.

Carbon Ink uses pigmented ink in order to improve the water-resisting property, light stability and heat-resisting properties while normal Black/Blue Black ink is water-based with dyes.
That is why the carbon ink is suitable for important documents such as official documents which need to be stored for a long time. Some people use the carbon ink to draw a rough design for a picture painted in watercolours or coloured inks because carbon ink is run-proof.

You should be careful, however, to deal with carbon ink in your fountain pen. 
Ultrafine particle carbon powder was included in the ink. 
Comparing to the ink water-based with dyes, it tends to be stopped up because particles are coarse. If you use your fountain pen with the carbon ink everyday, there may not come problems but in case you have long period to use the fountain pen, it will be clogged. 
It causes serious problem because it is not easy to clean the pen clogged with the ink and dried up.
Here are some tips about using carbon ink in your fountain pen.

(1) Please pull out the ink cartridge/converter you are using and clean the nib completely before you use the carbon ink. 
(2) If you do not use the fountain pen in carbon ink for more than one week, please pull out the ink and wash the ink converter thoroughly.

Please be careful when using as it is not easy to wash out of clothes