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.
Panel Lining for Gunpla 101 - Gunpla 101
Bandai Gundam Marker Fine Line (Black) [BANGM01] - HobbyTown
This is one of the GUNDAM MARKER of mechanical pencil type which uses 0.3mm extremely thin lead. You can do inking easily by tracing hollow lines in the mold. Inking makes modulated realistic atmosphere without painting. You can use a rubber eraser for the excess paint. This pencil is the most suitable for beginners to do inking.
Bandai GP01 Gundam Marker Black Liner Mechanical Pencil .3mm
If i panel line this little guy, what do i need to clean it up? : r/Gunpla
Mr.HOBBY Creos GUNDAM MARKER 33 COLOR SET GM01-GM410
Gundam Planet - Fine Point Gundam Marker for Panel Lines
MR.HOBBY Marker GM301 GM302 GM303 GSI Permeating Pen 3pcs Black Gray Brown Pour Type Oily Paint Pen for Plastic Model Kit - AliExpress
Metallic Model Gundam Markers - 6 Piece Set, Hobby Lobby
Replying to @outofstepdad gundam markers and gundam paint pens are per
Vintage Revell HOT ROD' Custom 57 Chevy Nomad Model Car Kit
Vintage Revell HOT ROD' Custom 57 Chevy Nomad Model Car Kit
Gundam Marker GM301 Black - Pour Type
GSI Creos Gundam Marker Pouring Inking Pen Set Detail Builders Parts GMS122