This is felt tipped or other porous-tipped pens and markers.
GSI Creos Gundam Marker Menuangkan Tinta Pena Set Detail Pembangun
Gundam Marker CLEAR GLOSS
Gundam paint marker sets - Arts & Crafts
Use for inking to trace hollow lines. It g gives the model a three-dimensional feeling and makes it appear more realistic. The effect is stronger when you choose the color to ink according to the color of the model parts. In general, you can use black for dark parts, grey for lighter parts and brown for red parts.
Bandai Gundam Marker Black Fine Line
Gundam Planet - Pour Type Gundam Marker for Panel Lines
Gundam Marker Black (Fine)
G Project - Panel lining! An easy yet effective way to give your
GSI CREOS GUNDAM MARKER SET EXTRA THIN TYPE (RENEWAL)
Gundam Marker Extra Thin Type for Panel Lines Set (Renewal) - NZ